Stone Sea Sanctuary, Myrkky Mainline - Redundant ExGFX in SP4

[Dr. Tapeworm the Horrible Thing]

Various rooms (161, 162, 163, E5, E9, EE, 130) in these levels use this graphics file (ExGFX131) in SP4. However, none of these rooms use anything that isn't already in the standard castle set (GFX03), so it could easily be replaced with that to shave off an unnecessary graphics file.

[Josiah Baldwin]

fix #160 (stone sea sanctuary)

→ <<cset 5c9fbbbdaf41>>