fs_config.c: remove setuid from procrank

procrank only exists on userdebug/eng builds. For those builds,
procrank can be executed by running "su 0 procrank" instead of
relying on the binary being setuid root. This reduces the number
of setuid binaries on Android and allows for the deletion of
SELinux policy to support this.

Bug: 18342188
Change-Id: I982283f2e0f6fbe5efaffc08501c1ec175f65373