Remove JCenter from the app.

- JCenter is one of the places from where we were getting libraries for the app, however JCenter is shutting down: https://jeroenmols.com/blog/2021/02/04/migratingjcenter/. We have to obtain our libraries from elsewhere, fortunatley all the libraries that we need are now available in MavenCentral.

build.gradle

@@ -29,17 +29,6 @@ allprojects {
         google()
         mavenCentral()
         maven { url 'https://plugins.gradle.org/m2/' }
-        // Limit which libraries can be obtained from JCenter to these ones specified below
-        jcenter() {
-            content {
-                includeModule("com.amitshekhar.android", "debug-db")
-                includeModule("com.amitshekhar.android", "debug-db-base")
-                includeModule("com.moldedbits.r2d2", "r2d2")
-                includeModule("me.dm7.barcodescanner", "zxing")
-                includeModule("me.dm7.barcodescanner", "core")
-                includeModule("com.andrognito.patternlockview", "patternlockview")
-            }
-        }
     }
 }