Revert of [Chromecast] Use base::FeatureList to control features. (pa…

…tchset chromium#7 id:120001 of https://codereview.chromium.org/2825873002/ )

Reason for revert:
cast_features_browsertest.cc is flaky on our internal CQ bot - it's unclear why this did not manifest on the Chromium trybots.

I assume that state persisting in the PrefService between tests is causing the flakiness. Reverting this patch until I understand the root cause.

Original issue's description:
> [Chromecast] Use base::FeatureList to control features.
>
> In Chromium, Finch-enabled features are controlled through base::FeatureList,
> a class which abstracts the experiment framework and developer overrides
> from client code. Though Chromecast's experiment framework is fundamentally
> different (in that it is server-driven) Cast builds can still make use of
> this class. Introduce some utilities to help.
>
> At boot-up, the pref store will be queried for experiment configs, which
> were cached to disk on the most recent config fetch from the last boot
> cycle. If a developer overrides these features from the command line,
> that value takes precedence. These features will be used to initialize
> base::FeatureList, which can then be statically queried from any client
> code that depends on //base.
>
> This patch does not actually introduce or convert any existing features
> to use this framework.
>
> BUG=714291
> BUG= internal b/35424335
>
> Review-Url: https://codereview.chromium.org/2825873002
> Cr-Commit-Position: refs/heads/master@{#466507}
> Committed: https://chromium.googlesource.com/chromium/src/+/ef03d2b9a67352094516f4e866373378fb961ee8

TBR=halliwell@chromium.org,maclellant@chromium.org,asvitkine@chromium.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=714291

Review-Url: https://codereview.chromium.org/2838813003
Cr-Commit-Position: refs/heads/master@{#467041}

chromecast/base/BUILD.gn

@@ -38,8 +38,6 @@ source_set("base") {
     "bind_to_task_runner.h",
     "cast_constants.cc",
     "cast_constants.h",
-    "cast_features.cc",
-    "cast_features.h",
     "cast_paths.cc",
     "cast_paths.h",
     "cast_resource.cc",
@@ -128,7 +126,6 @@ test("cast_base_unittests") {
   sources = [
     "alarm_manager_unittest.cc",
     "bind_to_task_runner_unittest.cc",
-    "cast_features_unittest.cc",
     "device_capabilities_impl_unittest.cc",
     "error_codes_unittest.cc",
     "path_utils_unittest.cc",