cleanup: join string literals that are already on one line
Thanks to Kyle for noticing this and for providing the regular
expression to run on the codebase.
This patch has been reviewed by the test suite and they approved of
it.
# skip-blame: fallout from mass reformatting
Differential Revision: https://phab.mercurial-scm.org/D7028
#require docutils gettext
$ $TESTDIR/check-gendoc zh_CN
checking for parse errors