devel/asmutils: Deprecate port

Latest upstream release is 19 years ago. Its release notes announce that
the software would eventually be replaced by a small Linux distribution
called a-Linux.
See https://asm.sourceforge.net/asmutils.html for more details.

The port is for i386 only, which is not a tier 1 platform for any
supported FreeBSD version.

The port does not build with GCC 14, which is soon to become GCC_DEFAULT
version. Set USE_GCC=13 so that it does not block GCC_DEFAULT version
update. [1]

PR: 284486 [1]