chore(theming): remove ThemingController from psalm deprecated baseline

The deprecated IConfig::getAppValue() calls in ThemingController have
been replaced with IAppConfig::getAppValueString(), so the baseline
suppression entry is no longer needed.

Signed-off-by: Anna Larch <anna@nextcloud.com>
AI-Assisted-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: miaulalala

build/psalm-baseline.xml

@@ -2583,11 +2583,6 @@
       <code><![CDATA[getAppValue]]></code>
     </DeprecatedMethod>
   </file>
-  <file src="apps/theming/lib/Controller/ThemingController.php">
-    <DeprecatedMethod>
-      <code><![CDATA[getAppValue]]></code>
-    </DeprecatedMethod>
-  </file>
   <file src="apps/theming/lib/Controller/UserThemeController.php">
     <DeprecatedMethod>
       <code><![CDATA[getUserValue]]></code>