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

This reverts commit b532bc9b which is
commit 8d91f3f8 upstream.

It breaks the current Android ABI, and if needed, can be brought back in
an abi-safe way in the future.

Bug: 161946584
Change-Id: I49cbae8dc7f22b61aa41240cc86c5e19e83f4a00
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>