remove unnecessary boolean literals (dart-archive/linter#3007)

* remove unnecessary boolean literals

* fmt

Author: pq

lib/src/ast.dart

@@ -422,7 +422,7 @@ class _ElementVisitorAdapter extends GeneralizingElementVisitor {
   @override
   void visitElement(Element element) {
     var visitChildren = processor(element);
-    if (visitChildren == true) {
+    if (visitChildren) {
       element.visitChildren(this);
     }
   }

lib/src/rules/avoid_positional_boolean_parameters.dart

@@ -68,7 +68,7 @@ class _Visitor extends SimpleAstVisitor<void> {
     if (declaredElement != null && !declaredElement.isPrivate) {
       var parametersToLint =
           node.parameters.parameters.where(_isFormalParameterToLint);
-      if (parametersToLint.isNotEmpty == true) {
+      if (parametersToLint.isNotEmpty) {
         rule.reportLint(parametersToLint.first);
       }
     }

lib/src/rules/valid_regexps.dart

@@ -59,7 +59,7 @@ class _Visitor extends SimpleAstVisitor<void> {
         return;
       }
 
-      bool isTrue(Expression e) => e is BooleanLiteral && e.value == true;
+      bool isTrue(Expression e) => e is BooleanLiteral && e.value;
 
       var unicode = args.any((arg) =>
           arg is NamedExpression &&

lib/src/test_utilities/annotation.dart

@@ -61,6 +61,5 @@ class Annotation implements Comparable<Annotation> {
 
 extension on String? {
   int? toInt() => this == null ? null : int.parse(this!);
-  String? toNullIfBlank() =>
-      this == null || this!.trim().isEmpty == true ? null : this;
+  String? toNullIfBlank() => this == null || this!.trim().isEmpty ? null : this;
 }