emp_config: Don't monkey-patch WORLD_X to be even

emp_config() silently truncates WORLD_X to even.  Drop that.  We could
flag odd WORLD_X as error, but we don't validate the other
configuration values, so why this one?  Instead document it needs to
be even.  WORLD_Y, too.

Signed-off-by: Markus Armbruster <armbru@pond.sub.org>

src/lib/common/emp_config.c

@@ -138,7 +138,6 @@ emp_config(char *file)
     fclose(fp);
 
 done:
-    WORLD_X &= ~1;		/* force even */
     if (set_paths(file) < 0)
 	return -1;