rtc-vp9: Allow scene detection for all speeds

Current code was disallowing scene detection for
speeds >= 8, to avoid any encode_time increase
(see comment in the code).

But we can expect the cost to be small even at speed 8,9,
and that concern on encode_time was from some time ago
before 8 and 9 were further optimized. And this is
needed for content with scene changes (see issue attached).
So allow scene detection now for all RTC speed settings (speed >= 5).

Bug: b/346846607
Change-Id: I678dbb88ff1399ed89b2bf9770ae9427e3044fc4

vp9/encoder/vp9_encoder.c

@@ -4098,16 +4098,14 @@ static int encode_without_recode_loop(VP9_COMP *cpi, size_t *size,
 #endif
 
   // Scene detection is always used for VBR mode or screen-content case.
-  // For other cases (e.g., CBR mode) use it for 5 <= speed < 8 for now
-  // (need to check encoding time cost for doing this for speed 8).
+  // For other cases (e.g., CBR mode) use it for 5 <= speed.
   cpi->rc.high_source_sad = 0;
   cpi->rc.hybrid_intra_scene_change = 0;
   cpi->rc.re_encode_maxq_scene_change = 0;
   if (cm->show_frame && cpi->oxcf.mode == REALTIME &&
       !cpi->disable_scene_detection_rtc_ratectrl &&
       (cpi->oxcf.rc_mode == VPX_VBR ||
-       cpi->oxcf.content == VP9E_CONTENT_SCREEN ||
-       (cpi->oxcf.speed >= 5 && cpi->oxcf.speed < 8)))
+       cpi->oxcf.content == VP9E_CONTENT_SCREEN || cpi->oxcf.speed >= 5))
     vp9_scene_detection_onepass(cpi);
 
   if (svc->spatial_layer_id == svc->first_spatial_layer_to_encode) {