test: fix freebsd10-64 CI failures

Remove unneeded timers from some tests and move others from parallel
testing to sequential testing.

This is to resolve test failures on freebsd10-64 on CI. The failures
are all due to timers firing later than expected. Timers firing later
than they are set for can happen on resource-constrained hosts and is
not a bug.

In general, it may be wise to put tests that depend on timing into
sequential testing rather than parallel testing, as the timing can
be affected by other simultaneously-running test processes.

Fixes: nodejs#8041
Fixes: nodejs#9227

test/parallel/test-dgram-send-callback-multi-buffer.js

@@ -6,13 +6,8 @@ const dgram = require('dgram');
 
 const client = dgram.createSocket('udp4');
 
-const timer = setTimeout(function() {
-  throw new Error('Timeout');
-}, common.platformTimeout(200));
-
 const messageSent = common.mustCall(function messageSent(err, bytes) {
   assert.equal(bytes, buf1.length + buf2.length);
-  clearTimeout(timer);
 });
 
 const buf1 = Buffer.alloc(256, 'x');

test/parallel/test-dgram-send-multi-buffer-copy.js

@@ -6,13 +6,8 @@ const dgram = require('dgram');
 
 const client = dgram.createSocket('udp4');
 
-const timer = setTimeout(function() {
-  throw new Error('Timeout');
-}, common.platformTimeout(200));
-
 const onMessage = common.mustCall(function(err, bytes) {
   assert.equal(bytes, buf1.length + buf2.length);
-  clearTimeout(timer);
 });
 
 const buf1 = Buffer.alloc(256, 'x');