Convert :source-api and :source-local to android library module (#3636)

- There's really no plan to support other platforms on this code base
- The "KMP" modules only had android target which is rather pointless
- `i18n` involves more work but given it has no actual code keeping it as is

source-api/src/main/kotlin/eu/kanade/tachiyomi/util/RxExtension.kt

@@ -0,0 +1,6 @@
+package eu.kanade.tachiyomi.util
+
+import rx.Observable
+import tachiyomi.core.common.util.lang.awaitSingle
+
+suspend fun <T> Observable<T>.awaitSingle(): T = awaitSingle()