ZTS: Change cp_stress to fit timings

cp_stress is getting killed on the new QEMU-based github runners
we're developing. The problem is that the Linux based runners
should do 10 RUNS, where the FreeBSD based runners only have 3
RUNS to succeed.

This patch removes this different handling of Linux and FreeBSD.
The cp_stress test is running fine in around 2 minutes now.

Signed-off-by: Tino Reichardt <milky-zfs@mcmilk.de>

tests/zfs-tests/tests/functional/cp_files/cp_stress.ksh

@@ -57,13 +57,8 @@ MYPWD="$PWD"
 cd /$TESTPOOL/cp_stress
 CPUS=$(get_num_cpus)
 
-if is_freebsd ; then
-	# 'seekflood' takes longer on FreeBSD and can timeout the test
-	RUNS=3
-else
-	RUNS=10
-fi
-
+# should run in ~2 minutes on Linux and FreeBSD
+RUNS=3
 for i in $(seq 1 $RUNS) ; do
 	# Each run takes around 12 seconds.
 	log_must $STF_SUITE/tests/functional/cp_files/seekflood 2000 $CPUS