Remove doom*set-indirect-buffer-filename hack

This was done to help the modeline build its file path in indirect
buffers, but this has been fixed by using buffer-base-buffer.

Both ui/modeline and ui/doom-modeline have been refactored to
accommodate this.

modules/ui/modeline/config.el

@@ -434,7 +434,7 @@ Meant for `+modeline-buffer-path-function'."
   :init "%b"
   :faces t
   (if buffer-file-name
-      (+modeline-build-path buffer-file-name)
+      (+modeline-build-path (buffer-file-name (buffer-base-buffer)))
     "%b"))
 
 (def-modeline-segment! +modeline-buffer-directory