Clean up hacky code in Parser.parseTopLevelMethod

This hack was needed to cover a short time period in 2020 where an
improvement to flow analysis had landed in master but hadn't yet
landed in the checked-in SDK that is used for presubmit checks.  We
are long past needing it anymore.

Change-Id: I0d0cd3d4d9829cc4b0798a07feaac09bb4929f31
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/291841
Reviewed-by: Jens Johansen <[email protected]>
Commit-Queue: Paul Berry <[email protected]>

Author: stereotype441

pkg/_fe_analyzer_shared/lib/src/parser/parser_impl.dart

@@ -3684,25 +3684,10 @@ class Parser {
     if (getOrSet != null && !inPlainSync && optional("set", getOrSet)) {
       reportRecoverableError(asyncToken, codes.messageSetterNotSync);
     }
-    // TODO(paulberry): code below is slightly hacky to allow for implementing
-    // the feature "Infer non-nullability from local boolean variables"
-    // (https://github.com/dart-lang/language/issues/1274).  Since the version
-    // of Dart that is used for presubmit checks lags slightly behind master,
-    // we need the code to analyze correctly regardless of whether local boolean
-    // variables cause promotion or not.  Once the version of dart used for
-    // presubmit checks has been updated, this can be cleaned up to:
-    //   bool isExternal = externalToken != null;
-    //   if (externalToken != null && !optional(';', token.next!)) {
-    //     reportRecoverableError(
-    //         externalToken, codes.messageExternalMethodWithBody);
-    //   }
-    bool isExternal = false;
-    if (externalToken != null) {
-      isExternal = true;
-      if (!optional(';', token.next!)) {
-        reportRecoverableError(
-            externalToken, codes.messageExternalMethodWithBody);
-      }
+    bool isExternal = externalToken != null;
+    if (isExternal && !optional(';', token.next!)) {
+      reportRecoverableError(
+          externalToken, codes.messageExternalMethodWithBody);
     }
     token = parseFunctionBody(
         token, /* ofFunctionExpression = */ false, isExternal);