Remove jcenter line from build.gradle.kts

[emanuelb]

Jcenter declared in file buildSrc/build.gradle.kts

phoenix/buildSrc/build.gradle.kts

Lines 1 to 3 in 1aac929

	repositories {
	jcenter()
	}

Jcenter service is closed (currently in read-only mode, no updates for packages will be made)
more details on needed migration:
https://developer.android.com/studio/build/jcenter-migration
https://blog.gradle.org/jcenter-shutdown

and here content on how to migrate:
https://jeroenmols.com/blog/2021/02/04/migratingjcenter/

probably one or both of below entries are needed:

        gradlePluginPortal()
        mavenCentral()