Changes core/execution_context/OWNERS.

This is a follow-up after:
https://chromium-review.googlesource.com/c/chromium/src/+/989693/10/third_party/WebKit/Source/core/execution_context/OWNERS#5

Change-Id: Ief8ee8755876bedd5241d3e5977dc37cea669e12
Reviewed-on: https://chromium-review.googlesource.com/1029995Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Yuki Shiino <yukishiino@chromium.org>
Cr-Commit-Position: refs/heads/master@{#553961}

third_party/blink/renderer/core/execution_context/OWNERS

 # execution_context OWNERS
-file://third_party/blink/renderer/bindings/OWNERS
+#
+# The owner list is made intentionally empty.
+# Ask core/OWNERS for code reviews.
 
-# TEAM: blink-reviews-bindings@chromium.org
-# COMPONENT: Blink>Bindings
+# TEAM: platform-architecture-dev@chromium.org
+# COMPONENT: Blink>Internals>Frames