RMB-815: Delete empty testing subproject

https://issues.folio.org/browse/RMB-815

The testing subproject became empty when the UtilityClassTester was moved to
okapi-testing.

Delete the RMB testing subproject.

Author: julianladisch

pom.xml

@@ -6,7 +6,6 @@
   <packaging>pom</packaging>
   <name>raml-module-builder</name>
   <modules>
-    <module>testing</module>
     <module>util</module>
     <module>postgres-testing</module>
     <module>dbschema</module>