Python: Remove getAnArg in DataFlow::CallCfgNode

Until we've had further discussion on what is the right approach to
naming (internal discussion in github/codeql-python-team#95)

Author: RasmusWL

python/ql/src/semmle/python/dataflow/new/internal/DataFlowPublic.qll

@@ -193,13 +193,6 @@ class CallCfgNode extends CfgNode {
 
   /** Gets the data-flow node corresponding to the named argument of the call corresponding to this data-flow node */
   Node getArgByName(string name) { result.asCfgNode() = node.getArgByName(name) }
-
-  /** Gets the data-flow node corresponding to an argument of the call corresponding to this data-flow node */
-  Node getAnArg() {
-    exists(int n | result = this.getArg(n))
-    or
-    exists(string name | result = this.getArgByName(name))
-  }
 }
 
 /**