include/sys_clock.h: consolidate identical branches in __ticks_to_ms

The two branches of the compile-time conditional are identical, so
they are consolidated and the conditional removed.

Just hygiene again.  No functional change.

Signed-off-by: Charles E. Youse <charles.youse@intel.com>

include/sys_clock.h

@@ -121,15 +121,8 @@ static ALWAYS_INLINE s32_t z_ms_to_ticks(s32_t ms)
 static inline u64_t __ticks_to_ms(s64_t ticks)
 {
 #ifdef CONFIG_SYS_CLOCK_EXISTS
-
-#ifdef _NEED_PRECISE_TICK_MS_CONVERSION
-	/* use 64-bit math to keep precision */
-	return (u64_t)ticks * MSEC_PER_SEC / (u64_t)CONFIG_SYS_CLOCK_TICKS_PER_SEC;
-#else
-	/* simple multiplication keeps precision */
-	return (u64_t)ticks * MSEC_PER_SEC / (u64_t)CONFIG_SYS_CLOCK_TICKS_PER_SEC;
-#endif
-
+	return (u64_t)ticks * MSEC_PER_SEC /
+	       (u64_t)CONFIG_SYS_CLOCK_TICKS_PER_SEC;
 #else
 	__ASSERT(ticks == 0, "ticks not zero");
 	return 0ULL;