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

This reverts commit 68156ce2 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: I7d958eaa72b5fb242f60899c024cbbd34e7cb140
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>