cleanup: fix some latent open(path).read() et al calls we previously missed
This pattern was banned by check-code way back in 1b4b82063ce2 (may of
2011), but due to a regular expression rewriting bug in check-code
these particular callsites were never detected. Python 3.7 caught the
bug, which then exposed these errors.
Differential Revision: https://phab.mercurial-scm.org/D2863
$ echo "[extensions]" >> $HGRCPATH
$ echo "mq=" >> $HGRCPATH
$ hg init
$ echo 'base' > base
$ hg ci -Ambase
adding base
$ hg qnew -mmqbase mqbase
$ hg qsave
$ hg qrestore 2
restoring status: hg patches saved state