fixes #18694

According to Autotools Mythbuster (https://autotools.io/libtool/lafiles.html)
libtool archive files are mostly vestigial, but they might create issues
when relocating binary packages as shown in #18694.

For GCC specifically, most distributions remove these files with
explicit commands:

https://git.stg.centos.org/rpms/gcc/blob/master/f/gcc.spec#_1303

Considered all of that, this commit adds an easy way for each
AutotoolsPackage to remove every .la file that has been installed.
The default, for the time being, is to maintain them - to be consistent
with what Spack was doing previously.