Auto merge of #5278 - alexcrichton:no-rustfmt-ci, r=alexcrichton

Remove rustfmt from Travis

As discussed at the recent work week this is probably a bit too zealous at this
time, so let's hold off on it until it's either more stable or we figure out a
better way to deal with changes in rustfmt.

For now though it'll hopefully be easy to continue running rustfmt every so
often!