Remove dead code guarded with "#if 0 … #endif" (#2338)

This code has been neutralized for many years now and served no purpose
other than cluttering up the code. We obviously don't need it and it's
out of date anyway.

If there's ever any reason to restore (parts of) it, we have git for
that. But we don't need to keep commented out code around.

include/workspace.h

@@ -50,17 +50,6 @@ void extract_workspace_names_from_bindings(void);
  */
 Con *create_workspace_on_output(Output *output, Con *content);
 
-#if 0
-/**
- * Sets the name (or just its number) for the given workspace. This has to
- * be called for every workspace as the rendering function
- * (render_internal_bar) relies on workspace->name and workspace->name_len
- * being ready-to-use.
- *
- */
-void workspace_set_name(Workspace *ws, const char *name);
-#endif
-
 /**
  * Returns true if the workspace is currently visible. Especially important for
  * multi-monitor environments, as they can have multiple currenlty active