#9 Patch to remove unused assembly functions from Tools sources

[Cameron Cawley]

riscos_var_val_alloc wasn't used anywhere, but because it was in the same source file as functions that are used, it would add a dependency on riscos_var_len, which is also unused. Removing both functions allows the patch in ticket #7 to be simplified since it's no longer necessary to build assembly sources in RISC OS builds.