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: I7880b8a9bcaa7392bae4d9b4222b0bfac659ceb0
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>