Revert "nvmem: Create a header for internal sharing"

This reverts commit 39dfc17a which is
commit ec9c08a1 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: I87a97fbac309c10538a89f683f6b7bd6bd7f7237
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>