Chore/gradle remove redundant apply (#135348)

I'm removing an unneded block of configuration from the `settings.gradle` template. It was introduced by me in #123511. At that time, I did not know that it's unnecessary, and did not test removing it – sorry about that.

I learned that it's unnecessary recently, when [I asked a question on StackOverflow](https://stackoverflow.com/questions/77073596/whats-the-difference-between-plugins-and-pluginmanagement-plugins-in). More context there.

dev/a11y_assessments/android/settings.gradle

@@ -13,10 +13,6 @@ pluginManagement {
     settings.ext.flutterSdkPath = flutterSdkPath()
 
     includeBuild("${settings.ext.flutterSdkPath}/packages/flutter_tools/gradle")
-
-    plugins {
-        id "dev.flutter.flutter-gradle-plugin" version "1.0.0" apply false
-    }
 }
 
 include ":app"

examples/hello_world/android/settings.gradle

@@ -24,13 +24,6 @@ pluginManagement {
         mavenCentral()
         gradlePluginPortal()
     }
-
-    plugins {
-        // Flutter Gradle Plugin's ID is defined in /packages/flutter_tools/gradle/build.gradle.kts.
-        // We set `apply false`, because we don't want to apply the plugin to
-        // the `android` root project, but only to the `app` subproject.
-        id "dev.flutter.flutter-gradle-plugin" version "1.0.0" apply false
-    }
 }
 
 plugins {

packages/flutter_tools/gradle/build.gradle.kts

@@ -18,6 +18,7 @@ gradlePlugin {
             id = "dev.flutter.flutter-gradle-plugin"
             implementationClass = "FlutterPlugin"
         }
+        // The "flutterAppPluginLoaderPlugin" name isn't used anywhere.
         create("flutterAppPluginLoaderPlugin") {
             id = "dev.flutter.flutter-plugin-loader"
             implementationClass = "FlutterAppPluginLoaderPlugin"

packages/flutter_tools/templates/app_shared/android.tmpl/settings.gradle.tmpl

@@ -15,10 +15,6 @@ pluginManagement {
         mavenCentral()
         gradlePluginPortal()
     }
-
-    plugins {
-        id "dev.flutter.flutter-gradle-plugin" version "1.0.0" apply false
-    }
 }
 
 plugins {