Revert "proc: Convert proc_mount to use mount_ns."

This reverts commit e94591d0.

This cleanup broke the parsing of procfs mount parameters.

Bug: 79705088
Change-Id: If13a2ebe3e0d993370f5d442addee2830d5b671b
Signed-off-by: Alistair Strachan <astrachan@google.com>
Git-commit: eff0c5c0
Git-repo: https://android.googlesource.com/kernel/common/


Signed-off-by: Sachin Grover <sgrover@codeaurora.org>