Remove mojo/common and all references to it

Bug: 799482
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel;master.tryserver.blink:linux_trusty_blink_rel;luci.chromium.try:linux_chromium_dbg_ng;master.tryserver.chromium.linux:linux_mojo;master.tryserver.chromium.linux:linux_vr
Change-Id: I976a9290ef77976187ce971e461814a887620ee2
Reviewed-on: https://chromium-review.googlesource.com/1028000
Commit-Queue: Oksana Zhuravlova <oksamyt@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Ken Rockot <rockot@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#554518}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 58de35c184c37407b779a98f95b27faa4adfdbf0

check_gn_headers_whitelist.txt

@@ -186,7 +186,6 @@ media/formats/mpeg/adts_stream_parser.h
 media/formats/mpeg/mpeg1_audio_stream_parser.h
 media/formats/mpeg/mpeg_audio_stream_parser_base.h
 media/gpu/media_gpu_export.h
-mojo/common/mojo_common_export.h
 mojo/edk/system/broker_messages.h
 mojo/edk/system/system_impl_export.h
 mojo/public/cpp/bindings/strong_associated_binding_set.h