compile.py: Don't set OFFICIAL_BUILD for --mode=official builds.
compile.py: Don't set OFFICIAL_BUILD for --mode=official builds.

As far as I can tell, no internal or external script looks at this env var
(there are several that look at CHROME_BUILD_TYPE though, which OFFICIAL_BUILD
is redundant with). This env var was added long ago (it was in initial.commit
and has only been moved around since), so it's probably no longer needed.

BUG=330631

Review URL: https://codereview.chromium.org/217833006

git-svn-id: 239fca9b83025a0b6f823aeeca02ba5be3d9fd76@261561 0039d316-1c4b-4281-b951-d872f2087c98

eunchong/build,eunchong/build,eunchong/build,eunchong/build