Change default component for src/ to Blink>JavaScript

The default component for src/ was Blink>JavaScript>Runtime
before. Unfortunately this is only partly true and tools
that use the information in the OWNERS file often misassign
issues because of it.

R=machenbach@chromium.org
NOTRY=true

Change-Id: I81457da1394a410fd494702f206af69857109c1c
Reviewed-on: https://chromium-review.googlesource.com/701758Reviewed-by: Michael Hablich <hablich@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Sergiy Byelozyorov <sergiyb@chromium.org>
Commit-Queue: Michael Hablich <hablich@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48315}

src/OWNERS

@@ -4,4 +4,4 @@ per-file intl.*=jshin@chromium.org
 per-file typing-asm.*=aseemgarg@chromium.org
 per-file typing-asm.*=bradnelson@chromium.org
 
-# COMPONENT: Blink>JavaScript>Runtime
+# COMPONENT: Blink>JavaScript