cleanup: remove pointless r-prefixes on single-quoted strings This is the promised second step on single-quoted strings. These had existed because our source transformer didn't turn r'' into b'', so we had tagged some strings as r-strings to get "native" strings on both Pythons. Now that the transformer is gone, we can dispense with this nonsense. Methodology: I ran hg locate 'set:added() or modified() or clean()' | egrep '.*\.py$' | xargs egrep --color=never -n -- \[\^b\]\[\^a-z\]r\'\[\^\'\\\\\]\*\'\[\^\'\ in an emacs grep-mode buffer, and then used a keyboard macro to iterate over the results and remove the r prefix as needed. # skip-blame removing unneeded r prefixes left over from Python 3 migration. Differential Revision: https://phab.mercurial-scm.org/D7306