Remove unused flag from the feature.gypi

Remove unused flag from the feature.gypi

Two flags - ENABLE_CSS_EXCLUSIONS and ENABLE_CSS_REGIONS - are not used.
Those features use runtime flag rather than compile flag currently.

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=160998

[dw.im, 2013-10-30 08:12:43]

feature.gypi file is the only file that the two flags are alive currently.
The flags are removed from all other files, already.

[abucur, 2013-10-30 15:45:30]

I'm fine with the change. It looks like CSS Regions is just under the
"experimental" flag in RuntimeEnabledFeatures. The same for CSS Exclusions. LGTM
from me.

[commit-bot: I haz the power, 2013-10-30 23:53:36]

No LGTM from a valid reviewer yet. Only full committers are accepted.
Even if an LGTM may have been provided, it was from a non-committer or
a lowly provisional committer, _not_ a full super star committer.
See http://www.chromium.org/getting-involved/become-a-committer
Note that this has nothing to do with OWNERS files.

[leviw_travelin_and_unemployed, 2013-10-31 00:25:09]

lgtm

[commit-bot: I haz the power, 2013-10-31 00:29:19]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/dw.im@samsung.com/52103003/1

[commit-bot: I haz the power, 2013-10-31 01:43:42]

Change committed as 160998