fix(android): remove deprecated jcenter() repository

jcenter has been sunset and is no longer supported. All dependencies
are available via mavenCentral() and google() repositories.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: kherembourg

example/android/app/build.gradle

@@ -117,7 +117,6 @@ repositories {
     mavenLocal()
     mavenCentral()
     google()
-    jcenter()
 }
 
 dependencies {

packages/purchasely/android/build.gradle

@@ -6,7 +6,6 @@ buildscript {
     google()
     mavenLocal()
     mavenCentral()
-    jcenter()
   }
 
   dependencies {
@@ -62,7 +61,6 @@ android {
 repositories {
   mavenLocal()
   mavenCentral()
-  jcenter()
   google()
 
   def found = false