It was only used to define -jN to control build parallelism. This is
now set automatically as of part 1 of this patch series and therefore
isn't needed.
Removes options that are now set by default (eg enable symbols, app=browser) and
those that have since been removed from configure (eg --disable-javaxpcom). Also
removes |--enable-jemalloc| if |--enable-trace-malloc| present, since the latter
force disables jemalloc regardless.
Note: This changeset is effectively no-op. No behaviour change is intended.
