Revert "Add "unknown" status for noise estimation."

This reverts commit e15fedb925.

Change-Id: Ibf2bce008c727a9754f88814b7630095fa7b8253

vp9/encoder/vp9_encodeframe.c

@@ -496,7 +496,7 @@ static void set_vbp_thresholds(VP9_COMP *cpi, int64_t thresholds[], int q) {
         threshold_base = 3 * threshold_base;
       else if (noise_level == kMedium)
         threshold_base = threshold_base << 1;
-      else if (noise_level == kLowLow)
+      else if (noise_level < kLow)
         threshold_base = (7 * threshold_base) >> 3;
     }
     if (cm->width <= 352 && cm->height <= 288) {

vp9/encoder/vp9_noise_estimate.c

@@ -25,7 +25,7 @@ void vp9_noise_estimate_init(NOISE_ESTIMATE *const ne,
                              int width,
                              int height) {
   ne->enabled = 0;
-  ne->level = kUnknown;
+  ne->level = kLowLow;
   ne->value = 0;
   ne->count = 0;
   ne->thresh = 90;
@@ -83,7 +83,7 @@ static void copy_frame(YV12_BUFFER_CONFIG * const dest,
 }
 
 NOISE_LEVEL vp9_noise_estimate_extract_level(NOISE_ESTIMATE *const ne) {
-  int noise_level = kUnknown;
+  int noise_level = kLowLow;
   if (ne->value > (ne->thresh << 1)) {
     noise_level = kHigh;
   } else {

vp9/encoder/vp9_noise_estimate.h

@@ -24,7 +24,6 @@ extern "C" {
 #endif
 
 typedef enum noise_level {
-  kUnknown,
   kLowLow,
   kLow,
   kMedium,