doc: fix dgram.md typos

socket.getRecvBufferSize() and socket.getSendBufferSize()
do not take any parameter

PR-URL: https://github.com/nodejs/node/pull/16183
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Yuta Hiroto <hello@about-hiroppy.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>

doc/api/dgram.md

@@ -226,14 +226,14 @@ never have reason to call this.
 If `multicastInterface` is not specified, the operating system will attempt to
 drop membership on all valid interfaces.
 
-### socket.getRecvBufferSize(size)
+### socket.getRecvBufferSize()
 <!-- YAML
 added: v8.7.0
 -->
 
 * Returns {number} the `SO_RCVBUF` socket receive buffer size in bytes.
 
-### socket.getSendBufferSize(size)
+### socket.getSendBufferSize()
 <!-- YAML
 added: v8.7.0
 -->