Python: Clean up a few verbose casts

python/ql/src/semmle/python/Concepts.qll

@@ -345,7 +345,7 @@ module HTTP {
         /** Gets the URL pattern for this route, if it can be statically determined. */
         string getUrlPattern() {
           exists(StrConst str |
-            DataFlow::exprNode(str).(DataFlow::LocalSourceNode).flowsTo(this.getUrlPatternArg()) and
+            this.getUrlPatternArg().getALocalSource() = DataFlow::exprNode(str) and
             result = str.getText()
           )
         }
@@ -478,9 +478,7 @@ module HTTP {
         /** Gets the mimetype of this HTTP response, if it can be statically determined. */
         string getMimetype() {
           exists(StrConst str |
-            DataFlow::exprNode(str)
-                .(DataFlow::LocalSourceNode)
-                .flowsTo(this.getMimetypeOrContentTypeArg()) and
+            this.getMimetypeOrContentTypeArg().getALocalSource() = DataFlow::exprNode(str) and
             result = str.getText().splitAt(";", 0)
           )
           or

python/ql/src/semmle/python/frameworks/Django.qll

@@ -1708,7 +1708,7 @@ private module PrivateDjango {
 
     DjangoRouteRegex() {
       this instanceof StrConst and
-      DataFlow::exprNode(this).(DataFlow::LocalSourceNode).flowsTo(rePathCall.getUrlPatternArg())
+      rePathCall.getUrlPatternArg().getALocalSource() = DataFlow::exprNode(this)
     }
 
     DjangoRegexRouteSetup getRouteSetup() { result = rePathCall }

python/ql/src/semmle/python/frameworks/Stdlib.qll

@@ -1097,7 +1097,7 @@ private DataFlow::CallCfgNode hashlibNewCall(string algorithmName) {
     result = API::moduleImport("hashlib").getMember("new").getACall() and
     nameArg in [result.getArg(0), result.getArgByName("name")] and
     exists(StrConst str |
-      DataFlow::exprNode(str).(DataFlow::LocalSourceNode).flowsTo(nameArg) and
+      nameArg.getALocalSource() = DataFlow::exprNode(str) and
       algorithmName = str.getText()
     )
   )

python/ql/src/semmle/python/frameworks/Tornado.qll

@@ -349,7 +349,7 @@ private module Tornado {
 
     TornadoRouteRegex() {
       this instanceof StrConst and
-      DataFlow::exprNode(this).(DataFlow::LocalSourceNode).flowsTo(setup.getUrlPatternArg())
+      setup.getUrlPatternArg().getALocalSource() = DataFlow::exprNode(this)
     }
 
     TornadoRouteSetup getRouteSetup() { result = setup }