Remove the 'gyp_config' concept from MB.

Remove the 'gyp_config' concept from MB.

Previously MB would try to ensure that the build directory
passed to it matched the expected gyp configuration for the bot
(i.e. that we would not pass "//out/Debug" as a path for a
release bot).

Making this work correctly was awkward for the Win x64 bots
(which use Release_x64 instead of Release), and it's not clear
that this check would ever actually catch a real problem.

So, this patch deletes all of the 'gyp_config' logic instead
and simplifies things.

TBR=scottmg@chromium.org
BUG=481692

Review URL: https://codereview.chromium.org/1348463002

Cr-Commit-Position: refs/heads/master@{#349043}