Every directory with a jar.mn now has JAR_MANIFESTS defined in its
moz.build file.
We also removed the may_skip special consideration of jar.mn files
because this information is now available during tier traversal by the
reader courtesy of the variables being present in moz.build files.
--HG--
extra : rebase_source : 21049b15e6bd9cf65b0805ccaccc4ba5aae93c98
extra : amend_source : 0b1ea866d725beef92d37c6f6d475369ac002e19
