Remove Bootstrap submodule.

It's not being used, and if needed in the future, a snapshot
of the code instead of a submodule will probably be
preferable. This is what we do with Foundation currently.

.gitmodules

@@ -1,9 +1,6 @@
 [submodule "engineer/static/engineer/lib/tweet"]
 	path = engineer/static/engineer/lib/tweet
 	url = https://github.com/seaofclouds/tweet.git
-[submodule "engineer/static/engineer/lib/bootstrap"]
-	path = engineer/static/engineer/lib/bootstrap
-	url = git://github.com/twitter/bootstrap.git
 [submodule "propane_distribution"]
 	path = propane_distribution
 	url = https://github.com/tylerbutler/propane-distribution.git