Remove redundant const qualifier

`ApplicationSetting::key()`, silences `-Wignored-qualifiers`

Author: savchenko

src/NotepadNext/ApplicationSettings.h

@@ -44,7 +44,7 @@ class ApplicationSetting
     {}
 
     inline T getDefault() const { return mCallable ? mCallable() : mDefault ; }
-    inline const char * const key() const { return mKey; }
+    inline const char * key() const { return mKey; }
 
 private:
     const char * const mKey;