remove invalid code from TRE

TRE wants to treat + and ? after a +, ?, or * as special; ? means
ungreedy and + is reserved for future use. however, this is
non-conformant. although redundant, these redundant characters have
well-defined (no-op) meaning for POSIX ERE, and are actually _literal_
characters (which TRE is wrongly ignoring) in POSIX BRE mode.

the simplest fix is to simply remove the unneeded nonstandard
functionality. as a plus, this shaves off a small amount of bloat.