Include mozconfig.rust in the common mozconfig so all jobs
will have the same rust config.
Automation mozconfigs all inherit from mozconfig.common,
so we can include mozconfig.rust there and not need it
anywhere else.
Remove --enable-rust from mozconfig.rust now that it's
the default. We only need the RUSTC and CARGO path
variables so jobs can find the toolchain installed from
the tooltool manifest. Also some automation jobs reject
the configure option if we set it unconditionally.
The --enable-rpath comment is no longer necessary; rust has
been consistently built this way for some time.
MozReview-Commit-ID: 2IeIIIinnPL
--HG--
extra : rebase_source : 79dadcc5ed13f2db312042d755a57698f267e902
The stable cargo now has all the features we need; pulling
a separate cargo nightly package is unnecessary.
MozReview-Commit-ID: FqWvSK0swsQ
--HG--
extra : rebase_source : 3659f8fa6d4a9a70c0731650aeced899519617f9
The unix mozconfig.rust is actually completely generic now that we're
using toolchains built with --enable-rpath in tooltool.
Move the mozconfig.rust fragment up a level to reduce confusion.
