powerpc/64s: restore_math remove TM test

The TM test in restore_math added by commit dc16b553 ("powerpc:
Always restore FPU/VEC/VSX if hardware transactional memory in use") is
no longer necessary after commit a8318c13 ("powerpc/tm: Fix
restoring FP/VMX facility incorrectly on interrupts"), which removed
the cases where restore_math has to restore if TM is active.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200623234139.2262227-1-npiggin@gmail.com