move getEnvVar function to common (#299)

utils/rocvideodecode/roc_video_dec.cpp

@@ -1104,15 +1104,3 @@ bool RocVideoDecoder::InitHIP(int device_id) {
     HIP_API_CALL(hipStreamCreate(&hip_stream_));
     return true;
 }
-
-int GetEnvVar(const char *name, int &dev_count) {
-    char *v = std::getenv(name);
-    if (v) {
-        char* p_tkn = std::strtok(v, ",");
-        while (p_tkn != nullptr) {
-            dev_count++;
-            p_tkn = strtok(nullptr, ",");
-        }
-    }
-    return dev_count;
-}