[TIMOB-28456] Android: Remove deprecated usage of jcenter() repo from gradle

*Summary:* The JCenter repository has been deprecated and their plan is to shut it down by February 1, 2022. https://developer.android.com/studio/build/jcenter-migration This impacts Android gradle builds which fetch dependencies from this repository. A "build.gradle" script references this repo via the jcenter() function. *To-Do:* Replace our usage of jcenter() with mavenCentral() here... https://github.com/appcelerator/titanium_mobile/blob/master/android/build.gradle https://github.com/appcelerator/titanium_mobile/blob/master/android/templates/build/root.build.gradle *Breaking-Change:* Changing our default templates from jcenter() to mavenCentral() might break module builds and hyperloop builds if the developer's "build.gradle" references a dependency that only exists in the deprecated jcenter() repo. If this is the case, then they can restore the deprecated behavior by re-adding the repo to their "build.gradle" as shown below. Just note that this will eventually stop working by February 2022.

// build.gradle
repositories {
	jcenter()
}