Revert "Make ping enforcing."

Causing adbd to run at 100% cpu utilization when the following
sequence of commands are run:

1) Run the command "adb shell ping -c 1 -w 5 www.google.com" for 5 times
2) Run "adb shell top -m 5"

The following denial occurs:

<5>[   20.647559] type=1400 audit(1389054327.861:21): avc:  denied  { sigchld } for  pid=1989 comm="adbd" scontext=u:r:ping:s0 tcontext=u:r:adbd:s0 tclass=process

Reverting for now.

This reverts commit 1b556c32.

Bug: 12251052
Change-Id: I1b9920624f49b0aed2226c41a45005aff228d9e8