Revert "mmc: core: add helpers mmc_regulator_enable/disable_vqmmc"

This reverts commit 38d32160 which is
commit 8d91f3f8 upstream.

It breaks the Android kernel abi and can be brought back in the future
in an abi-safe way if it is really needed.

Bug: 161946584
Change-Id: I67705a9f4b04cf051f9b0f1a3494284ae0122da2
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>