errors: remove duplicate error definition

Also fixes error being (now!) properly thrown by alphabetize-errors.

also properly enable lint rule

Was not using proper magic comment syntax before!

-URL: nodejs/node#15307
Reviewed-By: Myles Borins <myles.borins@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Yuta Hiroto <hello@about-hiroppy.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/internal/errors.js

@@ -261,16 +261,13 @@ E('ERR_SERVER_ALREADY_LISTEN',
 E('ERR_SOCKET_ALREADY_BOUND', 'Socket is already bound');
 E('ERR_SOCKET_BAD_BUFFER_SIZE', 'Buffer size must be a positive integer');
 E('ERR_SOCKET_BAD_PORT', 'Port should be > 0 and < 65536');
-E('ERR_SOCKET_BAD_BUFFER_SIZE', 'Buffer size must be a positive integer');
 E('ERR_SOCKET_BAD_TYPE',
   'Bad socket type specified. Valid types are: udp4, udp6');
 E('ERR_SOCKET_BUFFER_SIZE',
   (reason) => `Could not get or set buffer size: ${reason}`);
 E('ERR_SOCKET_CANNOT_SEND', 'Unable to send data');
 E('ERR_SOCKET_CLOSED', 'Socket is closed');
 E('ERR_SOCKET_DGRAM_NOT_RUNNING', 'Not running');
-E('ERR_SOCKET_BUFFER_SIZE',
-  (reason) => `Could not get or set buffer size: ${reason}`);
 E('ERR_STDERR_CLOSE', 'process.stderr cannot be closed');
 E('ERR_STDOUT_CLOSE', 'process.stdout cannot be closed');
 E('ERR_STREAM_WRAP', 'Stream has StringDecoder set or is in objectMode');