Moved gf_active code to encoder only

The gf_active code is only used by the encoder, so it was moved from
common and decoder.

Change-Id: Iada15acd5b2b33ff70c34668ca87d4cfd0d05025
diff --git a/vp8/encoder/ratectrl.c b/vp8/encoder/ratectrl.c
index 582c617..d328081 100644
--- a/vp8/encoder/ratectrl.c
+++ b/vp8/encoder/ratectrl.c
@@ -408,7 +408,7 @@
                   cpi->recent_ref_frame_usage[GOLDEN_FRAME] +
                   cpi->recent_ref_frame_usage[ALTREF_FRAME];
 
-    int pct_gf_active = (100 * cpi->common.gf_active_count) / (cpi->common.mb_rows * cpi->common.mb_cols);
+    int pct_gf_active = (100 * cpi->gf_active_count) / (cpi->common.mb_rows * cpi->common.mb_cols);
 
     // Reset the last boost indicator
     //cpi->last_boost = 100;
@@ -1022,7 +1022,7 @@
                       cpi->recent_ref_frame_usage[GOLDEN_FRAME] +
                       cpi->recent_ref_frame_usage[ALTREF_FRAME];
 
-        int pct_gf_active = (100 * cpi->common.gf_active_count) / (cpi->common.mb_rows * cpi->common.mb_cols);
+        int pct_gf_active = (100 * cpi->gf_active_count) / (cpi->common.mb_rows * cpi->common.mb_cols);
 
         // Reset the last boost indicator
         //cpi->last_boost = 100;