x86/Kconfig: Remove references to obsolete Kconfig symbols

Remove two symbols referenced in Kconfig which have been removed
previously by:

  ef3c67b6 ("mfd: intel_msic: Remove driver for deprecated platform")
  1b79fc4f ("x86/apb_timer: Remove driver for deprecated platform")

Detected by scripts/checkkconfigsymbols.py.

  [ bp: Merge into a single patch. ]

Suggested-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20210803113531.30720-5-lukas.bulwahn@gmail.com