[TIMOB-28377] Android: Remove deprecated usage of "ndk.dir" in "local.properties" file

*Summary:* As of Titanium 9.3.0, the following deprecation warning will be logged when build an Android app, module, or the Titanium SDK.

> Configure project :titanium
WARNING: NDK was located by using ndk.dir property. This method is deprecated and will be removed in a future release. Please delete ndk.dir from local.properties and set android.ndkVersion to [21.3.6528147] in all native modules in the project. https://developer.android.com/r/studio-ui/ndk-dir
NDK was located by using ndk.dir property. This method is deprecated and will be removed in a future release. Please delete ndk.dir from local.properties and set android.ndkVersion to [21.3.6528147] in all native modules in the project. https://developer.android.com/r/studio-ui/ndk-dir

*Reason:* Google has deprecated the "nki.dir" property in the "local.properties" file generated by Titanium. *Solution:* To be done on our end... * Remove our usage of the "ndk.dir" property. * Drop support of "ANDROID_NDK" environment variable for setting the NDK path. * Drop support of appc ti config setting android.ndkPath. * Do *NOT* set "build.gradle" setting "android.ndkVersion" in our template and use gradle's default NDK version. Allow app/module developer to override NDK version used via a custom "build.gradle" file as shown below.

// build.gradle
android {
	ndkVersion '21.2.6472646'
}