Remove use_gconf build flag

All usages of gconf have now been removed, so we can remove the build
flag too. After this, I will remove gconf from the instrumented
libraries, sysroots, and install-build-deps.sh.

Bug: 768027
Change-Id: Idf5e8d60da387b3287f875092feba488217ca642
Reviewed-on: https://chromium-review.googlesource.com/826046
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Tim Brown <timbrown@chromium.org>
Cr-Commit-Position: refs/heads/master@{#524120}
4 files changed