[Media Router] Remove MR FeatureSwitch's dependency on EAR.

[Media Router] Remove MR FeatureSwitch's dependency on EAR.

The ExtensionActionRedesign field trial	expires after M51, and the
feature is already enabled by default. We should remove MR's dependency
on it.

Also, remove media_router_with_cast_extension FeatureSwitch as it's no
longer used.

BUG=613252
Review-Url: https://codereview.chromium.org/1996123002
Cr-Commit-Position: refs/heads/master@{#395165}
(cherry picked from commit 9013e165f40d23f8fd28424f157fa4bb3805d018)

Committed: https://chromium.googlesource.com/chromium/src/+/94f2c95daa02e03ce1aef6f572abae74a857e8f5

[imcheng, 2016-05-23 20:17:12]

Description was changed from

==========
[Media Router] Remove MR FeatureSwitch's dependency on EAR.

The ExtensionActionRedesign field trial	expires after M51, and the
feature is already enabled by default. We should remove MR's dependency
on it.

Also, remove media_router_with_cast_extension FeatureSwitch as it's no
longer used.

BUG=613252

Review-Url: https://codereview.chromium.org/1996123002
Cr-Commit-Position: refs/heads/master@{#395165}
(cherry picked from commit 9013e165f40d23f8fd28424f157fa4bb3805d018)
==========

to

==========
[Media Router] Remove MR FeatureSwitch's dependency on EAR.

The ExtensionActionRedesign field trial	expires after M51, and the
feature is already enabled by default. We should remove MR's dependency
on it.

Also, remove media_router_with_cast_extension FeatureSwitch as it's no
longer used.

BUG=613252

Review-Url: https://codereview.chromium.org/1996123002
Cr-Commit-Position: refs/heads/master@{#395165}
(cherry picked from commit 9013e165f40d23f8fd28424f157fa4bb3805d018)

Committed:
https://chromium.googlesource.com/chromium/src/+/94f2c95daa02e03ce1aef6f572ab...
==========

[imcheng, 2016-05-23 20:17:13]

Committed patchset #1 (id:1) manually as
94f2c95daa02e03ce1aef6f572abae74a857e8f5.