Remove header file that doesn't exist from build files.

Followup to https://codereview.chromium.org/920963003 which removed
media/base/scoped_histogram_timer.h.

R=rkaplov@chromium.org,dalecurtis@chromium.org
BUG=459058

Review URL: https://codereview.chromium.org/948423002

Cr-Commit-Position: refs/heads/master@{#318016}

media/base/BUILD.gn

@@ -132,7 +132,6 @@ source_set("base") {
     "renderer_factory.h",
     "sample_format.cc",
     "sample_format.h",
-    "scoped_histogram_timer.h",
     "seekable_buffer.cc",
     "seekable_buffer.h",
     "serial_runner.cc",

media/media.gyp

@@ -345,7 +345,6 @@
         'base/renderer_factory.h',
         'base/sample_format.cc',
         'base/sample_format.h',
-        'base/scoped_histogram_timer.h',
         'base/seekable_buffer.cc',
         'base/seekable_buffer.h',
         'base/serial_runner.cc',