Undo PokeCodec's PRs

This commit undoes most of PokeCodec's PRs after the debate in chat. Some
harmless or completely superseded PRs have been left alone, as there is not
much benefit in attempting to undo them.

Reverts #1104, #1108, #1115, #1118, #1119, #1124, #1126, #1127, #1132, #1136,
#1137, #1139, #1140, #1144, #1148, #1149, #1150, #1153, #1155, #1177, #1179,
#1180, #1181, #1182 and #1183.

src/script.c

@@ -26,9 +26,9 @@ void InitScriptContext(struct ScriptContext *ctx, void *cmdTable, void *cmdTable
     s32 i;
 
     ctx->mode = 0;
-    ctx->scriptPtr = NULL;
+    ctx->scriptPtr = 0;
     ctx->stackDepth = 0;
-    ctx->nativePtr = NULL;
+    ctx->nativePtr = 0;
     ctx->cmdTable = cmdTable;
     ctx->cmdTableEnd = cmdTableEnd;
 
@@ -55,7 +55,7 @@ void SetupNativeScript(struct ScriptContext *ctx, bool8 (*ptr)(void))
 void StopScript(struct ScriptContext *ctx)
 {
     ctx->mode = 0;
-    ctx->scriptPtr = NULL;
+    ctx->scriptPtr = 0;
 }
 
 bool8 RunScriptCommand(struct ScriptContext *ctx)