debugfs: purge obsolete SRCU based removal protection

Purge the SRCU based file removal race protection in favour of the new,
refcount based debugfs_file_get()/debugfs_file_put() API.

Change-Id: I59adb0c01d9701438a32a97fb41d5decae8bf71e
Fixes: 49d200de ("debugfs: prevent access to removed files' private data")
Signed-off-by: Nicolai Stange <nicstange@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Git-commit: c9afbec27089cd6b4e621b639f41c7fc726c3bf1
Git-repo: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: Tingwei Zhang <tingwei@codeaurora.org>