Remove SamplingHint from the Sampling otep (open-telemetry#79)

* Remove SamplingHint from the Sampling otep

Signed-off-by: Bogdan Drutu <bogdandrutu@gmail.com>

* Update text/0006-sampling.md

Co-Authored-By: John Watson <jkwatson@gmail.com>

* Update text/0006-sampling.md

Co-Authored-By: John Watson <jkwatson@gmail.com>

Co-authored-by: John Watson <jkwatson@gmail.com>

text/0006-sampling.md

@@ -6,7 +6,6 @@
 This section tries to summarize all the changes proposed in this RFC:
  1. Move the `Sampler` interface from the API to SDK package. Apply some minor changes to the
  `Sampler` API.
- 1. Add a new `SamplerHint` concept to the API package.
  1. Add capability to record `Attributes` that can be used for sampling decision during the `Span`
  creation time.
  1. Remove `addLink` APIs from the `Span` interface, and allow recording links only during the span
@@ -68,9 +67,10 @@ Examples: gRPC, Express, Django developers.
 
 **Solution:**
 
- * On the start Span operation, the OpenTelemetry API will allow marking a span with one of three
- choices for the [SamplingHint](#samplinghint).
-
+* For the moment, the OpenTelemetry API will not offer any `SamplingHint` functionality for the last use case.
+This is intentional to avoid premature optimizations, and it is based on the fact that changing an API is
+backwards incompatible compared to adding a new API.
+
 ### Infrastructure package/binary developer
 Examples: HBase, Envoy developers.
 
@@ -170,26 +170,11 @@ distributed trace, and because of this OpenTelemetry API should NOT allow this c
 It is safe to assume that users of the API should only access the `RecordEvents` property when 
 instrumenting code and never access `SampledFlag` unless used in context propagators.
 
-### SamplingHint
-This is a new concept added in the OpenTelemetry API that allows to suggest sampling hints to the
-implementation of the API:
- * `NOT_RECORD`
-   * Suggest to not set (`RecordEvents = false`) and not propagate (`SampledFlag = false`).
- * `RECORD`
-   * Suggest to set (`RecordEvents = true`) but not propagate (`SampledFlag = false`).
- * `RECORD_AND_PROPAGATE`
-   * Suggest to set (`RecordEvents = true`) and propagate (`SampledFlag = true`).
-
-The default option for the span creation is to not have any suggestion (or suggestion is not
-specified). This can be implemented by using `null` as the default option or any language specific
-mechanism to achieve the same result.
-
 ### Sampler interface
 The interface for the Sampler class that is available only in the OpenTelemetry SDK:
  * `TraceID`
  * `SpanID`
  * Parent `SpanContext` if any
- * `SamplerHint`
  * `Links`
  * Span name
  * `SpanKind`
@@ -204,19 +189,13 @@ It produces an output called `SamplingResult` that includes:
 ### Default Samplers
 These are the default samplers implemented in the OpenTelemetry SDK:
  * ALWAYS_ON
-   * Ignores all values in SamplingHint.
  * ALWAYS_OFF
-   * Ignores all values in SamplingHint.
  * ALWAYS_PARENT
-   * Ignores all values in SamplingHint.
    * Trust parent sampling decision (trusting and propagating parent `SampledFlag`).
    * For root Spans (no parent available) returns `NOT_RECORD`.
  * Probability
-   * Allows users to configure to ignore or not the SamplingHint for every value different than 
-   `UNSPECIFIED`. 
-     * Default is to NOT ignore `NOT_RECORD` and `RECORD_AND_PROPAGATE` but ignores `RECORD`.
    * Allows users to configure to ignore the parent `SampledFlag`.
-   * Allows users to configure if probability applies only for "root spans", "root spans and remote 
+   * Allows users to configure if probability applies only for "root spans", "root spans and remote
    parent", or "all spans".
      * Default is to apply only for "root spans and remote parent".
      * Remote parent property should be added to the SpanContext see specs [PR/216][specs-pr-216]
@@ -229,7 +208,7 @@ These are the default samplers implemented in the OpenTelemetry SDK:
 |ALWAYS_ON|`True`|`True`|
 |ALWAYS_OFF|`False`|`False`|
 |ALWAYS_PARENT|`False`|`False`|
-|Probability|`SamplingHint==RECORD OR SampledFlag`|`SamplingHint==RECORD_AND_PROPAGATE OR Probability`|
+|Probability|`Same as SampledFlag`|`Probability`|
 
 **Child Span Decision:**
 
@@ -238,7 +217,7 @@ These are the default samplers implemented in the OpenTelemetry SDK:
 |ALWAYS_ON|`True`|`True`|
 |ALWAYS_OFF|`False`|`False`|
 |ALWAYS_PARENT|`ParentSampledFlag`|`ParentSampledFlag`|
-|Probability|`SamplingHint==RECORD OR SampledFlag`|`ParentSampledFlag OR SamplingHint==RECORD_AND_PROPAGATE OR Probability`|
+|Probability|`Same as SampledFlag`|`ParentSampledFlag OR Probability`|
 
 ### Links
 This RFC proposes that Links will be recorded only during the start `Span` operation, because: