refactor: remove omitProviderInModelName functionality and related localization

- Removed the omitProviderInModelName key from PreferenceKeys and its associated logic throughout the codebase.
- Updated SettingsService and AppSettings to eliminate references to the omitted provider functionality.
- Cleaned up related localization strings in multiple languages to reflect the removal of this feature.
- Enhanced code clarity and maintainability by streamlining settings management.

lib/core/persistence/persistence_migrator.dart

@@ -79,7 +79,6 @@ class PersistenceMigrator {
     copyBool(PreferenceKeys.largeText);
     copyBool(PreferenceKeys.darkMode);
     copyString(PreferenceKeys.defaultModel);
-    copyBool(PreferenceKeys.omitProviderInModelName);
     copyString(PreferenceKeys.voiceLocaleId);
     copyBool(PreferenceKeys.voiceHoldToTalk);
     copyBool(PreferenceKeys.voiceAutoSendFinal);
@@ -185,7 +184,6 @@ class PersistenceMigrator {
       PreferenceKeys.largeText,
       PreferenceKeys.darkMode,
       PreferenceKeys.defaultModel,
-      PreferenceKeys.omitProviderInModelName,
       PreferenceKeys.voiceLocaleId,
       PreferenceKeys.voiceHoldToTalk,
       PreferenceKeys.voiceAutoSendFinal,