[MNG-4991] LegacyRepositorySystem#injectProxy(repositories, proxies) doesn't evaluate non-proxy hosts

Remove empty override of 'it-defaults' profile because it breaks MNG-4645. It is
still reliable for both cases because:
before MNG-4645) It relied on the fact that the override removes the global
settings Maven Central definition of 'file:target/null' while Maven internally
still added canonical Maven Central back.
with MNG-4645) The empty profile override completely removes Maven Central
definition which means that the mirror won't proxy a non-existing repository.

This closes #95

Author: michael-o

core-it-suite/src/test/resources/mng-4991/settings-template.xml

@@ -37,13 +37,4 @@ under the License.
       <nonProxyHosts>@localhost@</nonProxyHosts>
     </proxy>
   </proxies>
-  <profiles>
-    <profile>
-      <id>it-defaults</id>
-      <!-- disable central override and use built-in values -->
-    </profile>
-  </profiles>
-  <activeProfiles>
-    <activeProfile>it-defaults</activeProfile>
-  </activeProfiles>
 </settings>