tests: Unmark socket-service test as flaky

This essentially reverts commit
cffed58737.

The preceding two commits have fixed the test so it’s no longer flaky.
The following command gives 5000 passes in a row for me:

meson test -C /opt/gnome/build/glib/ socket-service --repeat 5000

Signed-off-by: Philip Withnall <withnall@endlessm.com>

Fixes: #1679

gio/tests/meson.build

@@ -67,7 +67,7 @@ gio_tests = {
   'sleepy-stream' : {},
   'socket' : {},
   'socket-listener' : {},
-  'socket-service' : { 'suite': ['flaky'] },
+  'socket-service' : {},
   'srvtarget' : {},
   'task' : {},
   'vfs' : {},