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: I445c816cec4ea97b2f6f4abf516109f17b0f214a
Signed-off-by: Alistair Strachan <astrachan@google.com>
Git-commit: c396a018
Git-repo: https://android.googlesource.com/kernel/common/


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