Remove extraneous parens from function-type (#3856)

Author: srawlins

lib/src/render/element_type_renderer.dart

@@ -16,7 +16,7 @@ abstract class ElementTypeRenderer<T extends ElementType> {
   String wrapNullabilityParens(T elementType, String inner) =>
       elementType.nullabilitySuffix.isEmpty
           ? inner
-          : '($inner${elementType.nullabilitySuffix})';
+          : '$inner${elementType.nullabilitySuffix}';
 }
 
 // HTML implementations.

test/element_type_test.dart

@@ -171,12 +171,11 @@ void f(int Function(String)? p) {}
 
       expect(
         parameterType.linkedName,
-        // TODO(https://github.com/dart-lang/dartdoc/issues/2381): Fix.
-        '($intLink Function'
+        '$intLink Function'
         '<span class="signature">'
         '(<span class="parameter" id="param-">'
         '<span class="type-annotation">$stringLink</span>'
-        '</span>)</span>?)',
+        '</span>)</span>?',
       );
       expect(parameterType.nameWithGenerics, equals('Function'));
     });
@@ -190,11 +189,11 @@ void f(int Function<T>(T)? p) {}
 
       expect(
         parameterType.linkedName,
-        '($intLink Function'
+        '$intLink Function'
         '&lt;<wbr><span class="type-parameter">T</span>&gt;'
         '<span class="signature">'
         '(<span class="parameter" id="param-">'
-        '<span class="type-annotation">T</span></span>)</span>?)',
+        '<span class="type-annotation">T</span></span>)</span>?',
       );
       expect(
         parameterType.nameWithGenerics,