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/ui/setting/SettingsBrowseController.kt

@@ -2,7 +2,6 @@ package eu.kanade.tachiyomi.ui.setting
 
 import androidx.preference.PreferenceScreen
 import eu.kanade.tachiyomi.R
-import eu.kanade.tachiyomi.data.preference.asImmediateFlow
 import eu.kanade.tachiyomi.extension.ExtensionUpdateJob
 import eu.kanade.tachiyomi.util.preference.defaultValue
 import eu.kanade.tachiyomi.util.preference.infoPreference
@@ -11,7 +10,6 @@ import eu.kanade.tachiyomi.util.preference.preferenceCategory
 import eu.kanade.tachiyomi.util.preference.summaryRes
 import eu.kanade.tachiyomi.util.preference.switchPreference
 import eu.kanade.tachiyomi.util.preference.titleRes
-import kotlinx.coroutines.flow.launchIn
 import eu.kanade.tachiyomi.data.preference.PreferenceKeys as Keys
 
 class SettingsBrowseController : SettingsController() {
@@ -54,18 +52,6 @@ class SettingsBrowseController : SettingsController() {
                 summaryRes = R.string.requires_app_restart
                 defaultValue = true
             }
-            switchPreference {
-                key = Keys.showNsfwExtension
-                titleRes = R.string.pref_show_nsfw_extension
-                defaultValue = true
-            }
-            switchPreference {
-                key = Keys.labelNsfwExtension
-                titleRes = R.string.pref_label_nsfw_extension
-                defaultValue = true
-
-                preferences.showNsfwExtension().asImmediateFlow { isVisible = it }.launchIn(viewScope)
-            }
 
             infoPreference(R.string.parental_controls_info)
         }