remove dl_nonlazy global if unused in Dynaloader

Saves an int of memory per interp. Removes a env var lookup, and on Win32
also remove a registry check for PERL_DL_NONLAZY. This speeds up start up
time of interp a tiny bit. While platforms other than hpux and dlopen use
RTLD_LAZY, they use it unconditionally ignoring PERL_DL_NONLAZY. I am not
judging that decision in this commit.