Remove enable_media_router.

It was set to false only on iOS and cast, but the define is mostly used
in chrome/ which isn't used in neither iOS nor cast builds.

No intended behavior change.

BUG=461815,704958
TBR=cpu

Review-Url: https://codereview.chromium.org/2760403003
Cr-Original-Commit-Position: refs/heads/master@{#466043}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 678822e951c8943cc2b80657eeaec130d82b7385
1 file changed