Remove ndkPath from generated build.gradle

- Starting Unity 2023, Unity generates build.gradle with ndkPath
  which contains the absolute path to the NDK (e.g.
  `ndkPath "/Applications/Unity/Hub/Editor/2023.1.14f1/PlaybackEngines/AndroidPlayer/NDK"`).
  This causes the build to fail when tested on a different machine or
  when the ndk version is defined in the app level build.gradle.

Author: ricardodalarme

example/unity/DemoApp/Assets/FlutterUnityIntegration/Editor/Build.cs

@@ -330,6 +330,7 @@ private static void ModifyAndroidGradle(bool isPlugin)
             buildText = buildText.Replace("enableSplit = true", "enable true");
             buildText = buildText.Replace("implementation fileTree(dir: 'libs', include: ['*.jar'])", "implementation(name: 'unity-classes', ext:'jar')");
             buildText = buildText.Replace(" + unityStreamingAssets.tokenize(', ')", "");
+            buildText = Regex.Replace(buildText, "ndkPath \".*\"", "");
 
             if(isPlugin)
             {