Revert part of 64094e12 because mysqld_safe isn't just used for
Debian. As such references to specific packaging files like
/etc/mysql/debian.cnf shouldn't have passed a review.

There's also no history of why 64094e12 was needed based on
the history of debian/patches/38_scripts__mysqld_safe.sh__signals.dpatch

Other distos have survived without mysqld_safe handling signals.