Eliminate GN arg 'remove_webcore_debug_symbols'

It was replaced by blink_symbol_level ~2 years ago.

For the last month, gn gen has printed an error if this argument
is set. GN printed a warning for 1 month before that. Two months notice
seems sufficient.

Bug: 943869
Change-Id: I27c16ac6ebd03f5f1b93e153dd2258a89e50c5e1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1619244
Commit-Queue: James Cook <jamescook@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#661505}
1 file changed