kbuild: remove EXPERT and !COMPILE_TEST guarding from TRIM_UNUSED_KSYMS

This reverts the following two commits:

  - a555bdd0 ("Kbuild: enable TRIM_UNUSED_KSYMS again, with some guarding")
  - 5cf0fd59 ("Kbuild: disable TRIM_UNUSED_KSYMS option")

Commit 5e9e95cc ("kbuild: implement CONFIG_TRIM_UNUSED_KSYMS without
recursion") solved the build time issue.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>