Remove unused blink_gc_plugin_flags.py script.

Became unused with GN, now safe to remove.

R=dcheng,thakis
BUG=

Review-Url: https://codereview.chromium.org/2691943009
Cr-Original-Commit-Position: refs/heads/master@{#451056}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 114b2d6f5b9ce2206987fa8db489e2d2d05581b9
1 file changed