[Extensions Metrics] Stop recording InstallCause for unpack outcomes

Stop recording Extensions.UnpackSuccessInstallCause and
Extensions.UnpackFailureInstallCause. We haven't been looking at them
lately.

Bug: 975376
Change-Id: I3f1fac7fb981eaf8bb3c9fa23a96b8f9ab857db4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1703421
Reviewed-by: Robert Kaplow <rkaplow@chromium.org>
Commit-Queue: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#677959}

chrome/browser/extensions/crx_installer.cc

@@ -482,9 +482,6 @@ void CrxInstaller::OnUnpackFailure(const CrxInstallError& error) {
   UMA_HISTOGRAM_ENUMERATION("Extensions.UnpackFailureInstallSource",
                             install_source(), Manifest::NUM_LOCATIONS);
 
-  UMA_HISTOGRAM_ENUMERATION("Extensions.UnpackFailureInstallCause",
-                            install_cause(),
-                            extension_misc::NUM_INSTALL_CAUSES);
   ReportFailureFromFileThread(error);
 }
 
@@ -501,10 +498,6 @@ void CrxInstaller::OnUnpackSuccess(
                             install_source(), Manifest::NUM_LOCATIONS);
 
 
-  UMA_HISTOGRAM_ENUMERATION("Extensions.UnpackSuccessInstallCause",
-                            install_cause(),
-                            extension_misc::NUM_INSTALL_CAUSES);
-
   extension_ = extension;
   temp_dir_ = temp_dir;
   dnr_ruleset_checksum_ = dnr_ruleset_checksum;

tools/metrics/histograms/histograms.xml

@@ -42460,7 +42460,10 @@ uploading your change for review.
 </histogram>
 
 <histogram name="Extensions.UnpackFailureInstallCause"
-    enum="ExtensionInstallCause" expires_after="M77">
+    enum="ExtensionInstallCause">
+  <obsolete>
+    Stopped recording 2019-07.
+  </obsolete>
   <owner>extensions-core@chromium.org</owner>
   <summary>
     Count failing CRX installs, grouped by the way an extension can be
@@ -42479,7 +42482,10 @@ uploading your change for review.
 </histogram>
 
 <histogram name="Extensions.UnpackSuccessInstallCause"
-    enum="ExtensionInstallCause" expires_after="M77">
+    enum="ExtensionInstallCause">
+  <obsolete>
+    Stopped recording 2019-07.
+  </obsolete>
   <owner>extensions-core@chromium.org</owner>
   <summary>
     Count successful CRX installs, grouped by the cause of the install.