Removing entries from exec_script_whitelist

These entries are not using exec_script anymore so we can enforce the
check and remove them from the whitelist.

BUG=None
NOTRY=True

Review-Url: https://codereview.webrtc.org/2598403002
Cr-Commit-Position: refs/heads/master@{#15843}
diff --git a/.gn b/.gn
index ca3a6a7..3e0fcf2 100644
--- a/.gn
+++ b/.gn
@@ -48,9 +48,4 @@
 # These are the list of GN files that run exec_script. This whitelist exists
 # to force additional review for new uses of exec_script, which is strongly
 # discouraged except for gypi_to_gn calls.
-exec_script_whitelist = build_dotfile_settings.exec_script_whitelist + [
-                          "//third_party/boringssl/BUILD.gn",
-                          "//third_party/openh264/BUILD.gn",
-                          "//third_party/opus/BUILD.gn",
-                          "//webrtc/modules/video_render/BUILD.gn",
-                        ]
+exec_script_whitelist = build_dotfile_settings.exec_script_whitelist