Prefer direct expressions to EQUS

[Rangi42]

Here's an example. engine/events/mom_phone.asm defines DEF NUM_MOM_ITEMS_1 EQUS "((MomItems_1.End - MomItems_1) / 8)" and DEF NUM_MOM_ITEMS_2 EQUS "((MomItems_2.End - MomItems_2) / 8)". NUM_MOM_ITEMS_1 is only used once, in ld a, NUM_MOM_ITEMS_1. NUM_MOM_ITEMS_2 is used in two cp NUM_MOM_ITEMS_2. Neither of those EQUS definitions should exist -- just do ld a, (MomItems_1.End - MomItems_1) / 8 and cp (MomItems_2.End - MomItems_2) / 8.

This goes for EQUS more generally. The way the auto-expand is a misfeature of the assembly language, and we should avoid it when alternatives are possible. For example, DEF text EQUS "db TX_START," should really be MACRO text db TX_START, \# ENDM -- although it's two lines longer, it's more flexible (you could add checks inside for mistakes like text after line) and more future-proof (rgbasm eventually wants to remove EQUS expansion).

(The big exception is things like DEF tiles EQUS "* LEN_2BPP_TILE" so you can do ld bc, (7 * 7) tiles. Eventually rgbasm will have user-defined functions and we can replace it with DEF tiles(n) := n * LEN_2BPP_TILE to do ld bc, tiles(7 * 7)... but until then, the EQUS is okay.)