[v9_11] Drop FreeBSD 11

Support for FreeBSD 11.4, the last FreeBSD 11.x release, ended on September 30, 2021.

Link: https://www.freebsd.org/security/unsupported/

Also drop $WITH_READLINE_LIBEDIT from clang:freebsd13:amd64, it should not have been added.

(cherry picked from commit 981579f3)