There is no single bug that was reverted, as this work was done over
several bugs, including 1091668, 1123990, 1138535, and 1265272. Most
notable is that we are moving the precomplete generation back into
packager.py rather than spread out over various make variables (except
for the Windows installer, which is still specified in packager.mk).
MozReview-Commit-ID: KDcfR23kKr8