android: use mavenCentral instead of jcenter repository

From the `./gradlew --warning-mode all assembleStrippedUIEditingRelease`
output:

> > Configure project :
> The RepositoryHandler.jcenter() method has been deprecated. This is
> scheduled to be removed in Gradle 8.0. JFrog announced JCenter's sunset
> in February 2021. Use mavenCentral() instead. Consult the upgrading
> guide for further information:
> https://docs.gradle.org/7.2/userguide/upgrading_version_6.html#jcenter_deprecation
>         at build_a6ed945jjgv6miyybz50fclhq$_run_closure1$_closure2.doCall(/home/michi/development/git/libreoffice-WORKTREE-for-android-x86/android/source/build.gradle:14)
>         (Run with --stacktrace to get the full stack trace of this deprecation warning.)

Change-Id: I5db84a9778b598d1e3459dd313aa05c229060368
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/133239
Tested-by: Jenkins
Reviewed-by: Michael Weghorn <m.weghorn@posteo.de>

android/source/build.gradle

@@ -4,14 +4,14 @@ apply from: 'liboSettings.gradle'
 
 allprojects {
     repositories {
-        jcenter()
+        mavenCentral()
         google()
     }
 }
 //build-time dependencies - android plugin for gradle
 buildscript {
     repositories {
-        jcenter()
+        mavenCentral()
         google()
     }
     dependencies {