Avoid unnecessary malformed checking

Avoid unnecessary malformed checking

regen/regcharclass.pl can create macros for use where we need to worry
about the possibility of malformed UTF-8, and for where we don't.  In
the case of looking at regex patterns, the Perl core has complete
control over generating them, and hence isn't generally going to create
too short a buffer;  if it does, it's a bug that will show up and get
fixed.  This commit changes to generate and use the faster macros that
don't do bounds checking.