Remove use of OS provided random functions

We added the internal random generator a long time ago, and kept
the OS variant around as an opt-in feature with using use_os_rand=1.
We defaulted to using the fio provided one, and I doubt that
anyone has used the option.

The time has come to kill it.

Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/filesetup.c b/filesetup.c
index 43146ba..1b487d2 100644
--- a/filesetup.c
+++ b/filesetup.c
@@ -261,16 +261,9 @@
 	unsigned long long ret, sized;
 	unsigned long r;
 
-	if (td->o.use_os_rand) {
-		r = os_random_long(&td->file_size_state);
-		sized = td->o.file_size_high - td->o.file_size_low;
-		ret = (unsigned long long) ((double) sized * (r / (OS_RAND_MAX + 1.0)));
-	} else {
-		r = __rand(&td->__file_size_state);
-		sized = td->o.file_size_high - td->o.file_size_low;
-		ret = (unsigned long long) ((double) sized * (r / (FRAND_MAX + 1.0)));
-	}
-
+	r = __rand(&td->__file_size_state);
+	sized = td->o.file_size_high - td->o.file_size_low;
+	ret = (unsigned long long) ((double) sized * (r / (FRAND_MAX + 1.0)));
 	ret += td->o.file_size_low;
 	ret -= (ret % td->o.rw_min_bs);
 	return ret;