Revert "i2c: create debugfs entry per adapter"

This reverts commit 0e8926ab 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: I732949d96bc6cd124574d8a5ff3ed42f6d338791
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>