regcomp.c: Rmv malformed assert()

regcomp.c: Rmv malformed assert()

This had a plain '=' instead of an '==', thus setting the value in the
process of asserting it, hence would always be true.  But changing it to
'==' causes the assertion to fail in various cases.

I need to rethink this, so in the meantime am simply removing it.

Spotted by Dave Mitchell++