Clean up external repos

- Accept full URL as input instead, which allows for non-GitHub
- Remove automatic CDN fallback in favor of adding that as an external repo if needed

(cherry picked from commit 9c899e97a97480545d022974ffd3ea1248634155)

# Conflicts:
#	app/build.gradle.kts
#	app/src/main/java/eu/kanade/presentation/more/settings/screen/SettingsBrowseScreen.kt
#	app/src/main/java/eu/kanade/tachiyomi/extension/ExtensionManager.kt
#	app/src/main/java/eu/kanade/tachiyomi/ui/main/MainActivity.kt

app/src/main/java/exh/EXHMigrations.kt

@@ -653,6 +653,11 @@ object EXHMigrations {
                     // Deleting old download cache index files, but might as well clear it all out
                     context.cacheDir.deleteRecursively()
                 }
+                if (oldVersion under 60) {
+                    sourcePreferences.extensionRepos().getAndSet {
+                        it.map { "https://raw.githubusercontent.com/$it/repo" }.toSet()
+                    }
+                }
 
                 // if (oldVersion under 1) { } (1 is current release version)
                 // do stuff here when releasing changed crap