SVT encoder: comment out currently unused string constants

Author: farindk

libheif/plugins/encoder_svt.cc

@@ -76,10 +76,12 @@ static const char* kParam_speed = "speed";
 static const char* kParam_tune = "tune";
 static const char* const kParam_tune_valid_values[] = {"vq","psnr","ssim", nullptr};
 
+/*
 static const char* kParam_chroma = "chroma";
 static const char* const kParam_chroma_valid_values[] = {
     "420", "422", "444", nullptr
 };
+*/
 
 static int valid_tile_num_values[] = {1, 2, 4, 8, 16, 32, 64};