Many moz.build files define things that could be defined in parent
moz.build files. Keeping the number of moz.build files low helps with
build times due to less I/O and fewer directories traversed.
This patch eliminates a lot of moz.build files by moving their content
into parent moz.build files.
--HG--
extra : rebase_source : 0cfdf2697d10532e5b03cd27fbaadb41f42b837c
extra : amend_source : 0119d4e4881217f105e0e4ba1dfa9c8f7295f3e9
extra : histedit_source : eb49e62c67af2005fdc08d9c9a07f56bee98d558%2C50951e960e450f9b0e48fc7e8ec369d8666a63b0
