CPP: Deprecate Interface and remove the test.

cpp/ql/src/semmle/code/cpp/Class.qll

@@ -1116,8 +1116,9 @@ class PartialClassTemplateSpecialization extends ClassTemplateSpecialization {
  * };
  * ```
  * 
+ * DEPRECATED: This class is considered to be too specific for general usage.
  */
-class Interface extends Class {
+deprecated class Interface extends Class {
   Interface() {
     forex(Declaration m | m.getDeclaringType() = this.getABaseClass*() and not compgenerated(unresolveElement(m)) | m instanceof PureVirtualFunction)
   }

cpp/ql/test/library-tests/virtual_functions/virtual_functions/interfaces.expected

@@ -1 +0,0 @@
-| virtual_functions.cpp:1:7:1:7 | A |

cpp/ql/test/library-tests/virtual_functions/virtual_functions/interfaces.ql

@@ -1,4 +0,0 @@
-import cpp
-
-from Interface i
-select i