mm/mmu_gather: remove unused __tlb_remove_page()

Nobody is using __tlb_remove_page() now, clean it up.

And also remove the code comment above tlb_remove_page() because it's not
meaningful any more.

Link: https://lkml.kernel.org/r/Z6si0/A/zzEF/bFJ@MiWiFi-R3L-srv


Signed-off-by: Baoquan He <bhe@redhat.com>
Reviewed-by: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@kernel.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>