Reduce memory assigned to Surefire

We may need to reintroduce this change in the future, but for now we can
keep the configuration in sync with other parent POMs.

pom.xml

@@ -73,10 +73,7 @@
             -XX:TieredStopAtLevel=1
             <!-- We cap memory usage. This is especially relevant on Travis CI,
             but locally this should also be more than enough. -->
-            <!-- XXX: RefasterCheckTest` requires more memory, so here we use
-            more than in other projects. Review how to reconcile this. (Extra
-            property?) -->
-            -Xmx1024m
+            -Xmx512m
             <!-- This argument cannot be set through Surefire's
             'systemPropertyVariables' configuration setting. Setting the file
             encoding is necessary because forked unit test invocations