Remove ehcache (at least temporarily)

The fact that it was still there on the classpath means it needs to
be configured (and fails silently if you don't). Removed to give
us some tmie to reconsider.

pom.xml

@@ -79,16 +79,6 @@
       <scope>runtime</scope>
     </dependency>
 
-    <!-- EhCache -->
-    <dependency>
-      <groupId>javax.cache</groupId>
-      <artifactId>cache-api</artifactId>
-    </dependency>
-    <dependency>
-      <groupId>org.ehcache</groupId>
-      <artifactId>ehcache</artifactId>
-    </dependency>
-
     <!-- webjars -->
     <dependency>
       <groupId>org.webjars</groupId>