config: don't enable H.264 by default on P2P

We are not actively testing it and it currently crashes Chrome 83+ when insertable streams are used.

config.js

 
         // If set to true, it will prefer to use H.264 for P2P calls (if H.264
         // is supported).
-        preferH264: true
+        // preferH264: true
 
         // If set to true, disable H.264 video codec by stripping it out of the
         // SDP.