Revert r273099 "If the revision number starts with r, drop it. It will get added back"

This doesn't seem to work with Bash:

$ /work/llvm/utils/release/merge.sh --proj llvm --rev r275870
/work/llvm/utils/release/merge.sh: line 34: ${$1#r}: bad substitution

I get the same error with and without a leading 'r'.

llvm-svn: 275898