Unify NSFW flagging for sources/extensions

Since multisource extensions are no longer a thing, we now simply rely on the flag at the extension level, i.e. the per-Source/SourceFactory `@Nsfw` annotation is no longer checked.
We'll have to remove all of the annotation usages from the existing sources, which will also effectively break the setting for older versions of the app.

app/src/main/java/eu/kanade/tachiyomi/extension/util/ExtensionLoader.kt

@@ -6,7 +6,6 @@ import android.content.pm.PackageInfo
 import android.content.pm.PackageManager
 import androidx.core.content.pm.PackageInfoCompat
 import dalvik.system.PathClassLoader
-import eu.kanade.tachiyomi.annotations.Nsfw
 import eu.kanade.tachiyomi.data.preference.PreferencesHelper
 import eu.kanade.tachiyomi.extension.model.Extension
 import eu.kanade.tachiyomi.extension.model.LoadResult
@@ -154,13 +153,7 @@ internal object ExtensionLoader {
                 try {
                     when (val obj = Class.forName(it, false, classLoader).newInstance()) {
                         is Source -> listOf(obj)
-                        is SourceFactory -> {
-                            if (isSourceNsfw(obj)) {
-                                emptyList()
-                            } else {
-                                obj.createSources()
-                            }
-                        }
+                        is SourceFactory -> obj.createSources()
                         else -> throw Exception("Unknown source class type! ${obj.javaClass}")
                     }
                 } catch (e: Throwable) {
@@ -168,7 +161,6 @@ internal object ExtensionLoader {
                     return LoadResult.Error(e)
                 }
             }
-            .filter { !isSourceNsfw(it) }
 
         val langs = sources.filterIsInstance<CatalogueSource>()
             .map { it.lang }
@@ -215,22 +207,4 @@ internal object ExtensionLoader {
             null
         }
     }
-
-    /**
-     * Checks whether a Source or SourceFactory is annotated with @Nsfw.
-     */
-    private fun isSourceNsfw(clazz: Any): Boolean {
-        if (loadNsfwSource) {
-            return false
-        }
-
-        if (clazz !is Source && clazz !is SourceFactory) {
-            return false
-        }
-
-        // Annotations are proxied, hence this janky way of checking for them
-        return clazz.javaClass.annotations
-            .flatMap { it.javaClass.interfaces.map { it.simpleName } }
-            .firstOrNull { it == Nsfw::class.java.simpleName } != null
-    }
 }