Revert "i2c: create debugfs entry per adapter"

This reverts commit 4a2be5a7 which is
commit 73febd77 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: I387a39c568c604e0c63b6cd77d6bee76f4eaa936
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>