Don't leave root dumpstate-stats.txt

When booting the device after FDR, dumpstate triggers a BR with bugreport_mode=
BUGREPORT_ONBOARDING, which creates some temp files and dumpstate-stats.txt.
But, there are two files, -png.tmp and dumpstate-stats.txt, were remained as root
owner which prevents moving the files to /sdcard.

Bug: 425408179
Test: Boot and move files
Flag: EXEMPT bugfix
Change-Id: I8ea0bdcb7b40c5869142c1fd3ad5da224aaafd46
Signed-off-by: Jaegeuk Kim <jaegeuk@google.com>