Reverts "Warn when Gradle plugins are applied using the legacy "apply script method" way" (#140102)

Reverts flutter/flutter#139690
Initiated by: hellohuanlin
This change reverts the following previous change:
Original Description:
This PR adds a deprecation message when Android build is using the legacy "apply script method" way of applying Flutter's Gradle plugins (that is: [`flutter.gradle`](https://github.com/flutter/flutter/blob/3.16.0/packages/flutter_tools/gradle/flutter.gradle) and [`app_plugin_loader.gradle`](https://github.com/flutter/flutter/blob/3.16.0/packages/flutter_tools/gradle/app_plugin_loader.gradle)).

See also:
- #121541
  - in particular flutter/flutter#121541 (comment)
- #135392
  - and PR that add the migration guide: [flutter#9857](flutter/website#9857)

- I think either `logger.error` or `logger.quiet` must be used, because all other error levels are not shown during `flutter build apk` (and that's what most people use).

Author: auto-submit[bot]

packages/flutter_tools/gradle/app_plugin_loader.gradle

@@ -5,11 +5,5 @@
 // This file exists solely for the compatibility with projects that have
 // not migrated to the declarative apply of the Flutter App Plugin Loader Gradle Plugin.
 
-logger.error("You are applying Flutter's app_plugin_loader Gradle plugin \
-imperatively using the apply script method, which is deprecated and will be \
-removed in a future release. Migrate to applying Gradle plugins with the \
-declarative plugins block: https://flutter.dev/go/flutter-gradle-plugin-apply\n\
-")
-
 def pathToThisDirectory = buildscript.sourceFile.parentFile
 apply from: "$pathToThisDirectory/src/main/groovy/app_plugin_loader.groovy"

packages/flutter_tools/gradle/flutter.gradle

@@ -5,10 +5,5 @@
 // This file exists solely for the compatibility with projects that have
 // not migrated to the declarative apply of the Flutter Gradle Plugin.
 
-logger.error("You are applying Flutter's main Gradle plugin imperatively using \
-the apply script method, which is deprecated and will be removed in a future \
-release. Migrate to applying Gradle plugins with the declarative plugins \
-block: https://flutter.dev/go/flutter-gradle-plugin-apply\n")
-
 def pathToThisDirectory = buildscript.sourceFile.parentFile
 apply from: "$pathToThisDirectory/src/main/groovy/flutter.groovy"