Remove attempts to use NetBSD __weak_alias macros to export _-prefixed
versions of various fp[sg]et* symbols under softfloat. __weak_alias
isn't defined so we didn't export them and thus the Symbol.map entries
were wrong.
Reviewed by: jhibbits
Differential Revision: https://reviews.freebsd.org/D44327
The arm, mips, and riscv MD Symbol.map files listed some (but not all)
of the softfloat symbols that were actually defined in softfloat.c.
While here, also remove entries for __fixuns[sd]fsi which are provided
by libcompiler_rt and not by libc.
Sponsored by: DARPA / AFRL