Remove unneeded analyzer ignores (#7109)

We don't need these anymore.

examples/flutter_gallery/lib/demo/expansion_panels_demo.dart

@@ -10,7 +10,7 @@ enum _Location {
   Bermuda
 }
 
-typedef Widget DemoItemBodyBuilder(DemoItem<dynamic> item);
+typedef Widget DemoItemBodyBuilder<T>(DemoItem<T> item);
 typedef String ValueToString<T>(T value);
 
 class DualHeaderWithHint extends StatelessWidget {
@@ -152,7 +152,7 @@ class DemoItem<T> {
 
   final String name;
   final String hint;
-  final DemoItemBodyBuilder builder;
+  final DemoItemBodyBuilder<T> builder;
   final ValueToString<T> valueToString;
   T value;
   bool isExpanded = false;
@@ -189,7 +189,7 @@ class _ExpansionPanelsDemoState extends State<ExpasionPanelsDemo> {
         value: 'Caribbean cruise',
         hint: 'Change trip name',
         valueToString: (String value) => value,
-        builder: (DemoItem<String> item) { // ignore: argument_type_not_assignable, https://github.com/flutter/flutter/issues/5771
+        builder: (DemoItem<String> item) {
           void close() {
             setState(() {
               item.isExpanded = false;
@@ -223,7 +223,7 @@ class _ExpansionPanelsDemoState extends State<ExpasionPanelsDemo> {
         value: _Location.Bahamas,
         hint: 'Select location',
         valueToString: (_Location location) => location.toString().split(".")[1],
-        builder: (DemoItem<_Location> item) { // ignore: argument_type_not_assignable, https://github.com/flutter/flutter/issues/5771
+        builder: (DemoItem<_Location> item) {
           void close() {
             setState(() {
               item.isExpanded = false;
@@ -293,7 +293,7 @@ class _ExpansionPanelsDemoState extends State<ExpasionPanelsDemo> {
         value: 80.0,
         hint: 'Select sun level',
         valueToString: (double amount) => '${amount.round()}',
-        builder: (DemoItem<double> item) { // ignore: argument_type_not_assignable, https://github.com/flutter/flutter/issues/5771
+        builder: (DemoItem<double> item) {
           void close() {
             setState(() {
               item.isExpanded = false;

packages/flutter/lib/src/material/list_item.dart

@@ -209,7 +209,6 @@ class ListItem extends StatelessWidget {
         height: itemHeight,
         padding: const EdgeInsets.symmetric(horizontal: 16.0),
         child: new Row(
-          crossAxisAlignment: CrossAxisAlignment.center,
           children: children
         )
       )

packages/flutter/lib/src/services/image_resolution.dart

@@ -142,9 +142,9 @@ class AssetImage extends AssetBundleImageProvider {
     if (json == null)
       return null;
     // TODO(ianh): JSON decoding really shouldn't be on the main thread.
-    final Map<dynamic, dynamic> parsedManifest = JSON.decode(json);
+    final Map<String, List<String>> parsedManifest = JSON.decode(json);
     // TODO(ianh): convert that data structure to the right types.
-    return new SynchronousFuture<Map<dynamic, dynamic>>(parsedManifest); // ignore: return_of_invalid_type, https://github.com/flutter/flutter/issues/5771
+    return new SynchronousFuture<Map<String, List<String>>>(parsedManifest);
   }
 
   String _chooseVariant(String main, ImageConfiguration config, List<String> candidates) {

packages/flutter/lib/src/widgets/unique_widget.dart

@@ -25,7 +25,7 @@ abstract class UniqueWidget<T extends State<StatefulWidget>> extends StatefulWid
   /// The [key] argument cannot be null because it identifies the unique
   /// inflated instance of this widget.
   UniqueWidget({
-    @required GlobalKey key
+    @required GlobalKey<T> key
   }) : super(key: key) {
     assert(key != null);
   }
@@ -37,7 +37,7 @@ abstract class UniqueWidget<T extends State<StatefulWidget>> extends StatefulWid
   ///
   /// Might be null if the widget is not currently in the tree.
   T get currentState {
-    GlobalKey globalKey = key;
-    return globalKey.currentState; // ignore: return_of_invalid_type, https://github.com/flutter/flutter/issues/5771
+    GlobalKey<T> globalKey = key;
+    return globalKey.currentState;
   }
 }