Revert "Work around clang-cl bug to fix media_unittests link failure"

This reverts commit 6489c3bf.

Reason for revert:
Clang has rolled past r315330 (in #508804), so the work-around
is not necessary anymore.

Original change's description:
> Work around clang-cl bug to fix media_unittests link failure
> 
> TBR=wolenetz
> 
> Bug: 771710
> Cq-Include-Trybots: master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
> Change-Id: Id2de82dfda1fc003ed3a8095ad000e7a21f3feb9
> Reviewed-on: https://chromium-review.googlesource.com/701456
> Commit-Queue: Hans Wennborg <hans@chromium.org>
> Reviewed-by: Matthew Wolenetz <wolenetz@chromium.org>
> Reviewed-by: Nico Weber <thakis@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#506554}

TBR=thakis@chromium.org,wolenetz@chromium.org,hans@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 771710
Change-Id: I6916002fd569007a006ccf25285ee1dcf33159d7
Cq-Include-Trybots: master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Reviewed-on: https://chromium-review.googlesource.com/724339Reviewed-by: Hans Wennborg <hans@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#509679}

media/filters/source_buffer_stream.cc

@@ -13,7 +13,6 @@
 #include "base/logging.h"
 #include "base/memory/ptr_util.h"
 #include "base/trace_event/trace_event.h"
-#include "build/build_config.h"
 #include "media/base/media_switches.h"
 #include "media/base/timestamp_constants.h"
 #include "media/filters/source_buffer_platform.h"
@@ -232,9 +231,6 @@ template <typename RangeClass>
 SourceBufferStream<RangeClass>::~SourceBufferStream() {}
 
 template <>
-#if defined(__clang__) && defined(OS_WIN)
-MEDIA_EXPORT  // TODO(crbug.com/771710): Remove once clang-cl is fixed.
-#endif
 void SourceBufferStream<SourceBufferRangeByDts>::OnStartOfCodedFrameGroup(
     DecodeTimestamp coded_frame_group_start_dts,
     base::TimeDelta coded_frame_group_start_pts) {
@@ -246,9 +242,6 @@ void SourceBufferStream<SourceBufferRangeByDts>::OnStartOfCodedFrameGroup(
 }
 
 template <>
-#if defined(__clang__) && defined(OS_WIN)
-MEDIA_EXPORT  // TODO(crbug.com/771710): Remove once clang-cl is fixed.
-#endif
 void SourceBufferStream<SourceBufferRangeByPts>::OnStartOfCodedFrameGroup(
     DecodeTimestamp coded_frame_group_start_dts,
     base::TimeDelta coded_frame_group_start_pts) {