Revert "MIPS: add PMD table accounting into MIPS'pmd_alloc_one"

This reverts commit fc5705b2 which is
commit ed914d48b6a1040d1039d371b56273d422c0081e upstream.

Commit b2b29d6d011944 (mm: account PMD tables like PTE tables) is
introduced between v5.9 and v5.10, so this fix (commit 002d8b395fa1)
should NOT apply to any pre-5.10 branch.

Signed-off-by: Huang Pei <huangpei@loongson.cn>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>