the directory by default is not r/w and using rm(deleting-unlinking) on a file inside the directory should require r/w access.root is required to chmod the directory.

Erm... if anything---- id root the phone .then boot to recovery and try adb while in recovery. That said , you can't get # with su while the phone is fully booted anyway because you can't get past lockscreen to grant su access with the onscreen dialogue prompt.in recovery su is granted on the fly..

 

Wait a min here.........

/data/system is r/w by default...

Twas thinking of rootdir/system...

if you have busybox installed try busybox rm blah blah
Possible the applet is not included in stock..