kern: Remove gcc2_compiled stripping

Bruce added stripping of gcc2_compiled and other symbols when he made
the boot loader load the symbols for the kernel in 1995 (b5d89ca8ade3)
before the FreeBSD 2.1 release. This was copied around a bit and
tweaked over the years, but these symbols aren't produced by clang, nor
gcc12. The were to support dbx for a.out stabs format. gcc removed them
with stabs support last year. gcc 2.95.4 in FreeBSD 4.x continued to
emit these symbols unconditionally (it was missing a test for aout vs
elf it would appaer). They disappeared entirely with gcc 3.2.4 in 5.x
for all non a.out builds, and entirely in FreeBSD 6.x which had gcc
3.2.6.

Sponsored by: Netflix
Differential Revision: https://reviews.freebsd.org/D38764