Using PROG instead of PROGS will in cases of high -j with -DNO_ROOT cause
the PROG to show up more than once as it's handling the SCRIPTS install case
in a recursive manner, separate from the non-recursive case
After the recent batch of commits to bsd.progs.mk to fix behavior with how
variables are defaulted to, explicitly setting SRCS for a PROG is no longer
required
MFC after: 1 week
Reviewed by: asomers
Phabric: D1130
Sponsored by: EMC / Isilon Storage Division
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