Revert "fixup! proc: make oom adjustment files user read-only"

CTS no longer expects oom_{adj,score_adj} to be read-only.  See
https://android-review.googlesource.com/530687/

 for additional context.

This reverts commit 87a7a2cf.

Bug: 63142211
Change-Id: I1d1b33c93ca6b6c16a9c1d5430dcb5cbe3ec894c
Signed-off-by: Greg Hackmann <ghackmann@google.com>