Drop two #defines that never did anything

sgp/video.cpp guards _MT with #ifndef and then defines it 26 lines into the
file, long after every header that could read it, and both cl and clang-cl
already define _MT for the static runtime this project links. jascreens.cpp
defines _UNICODE after its last include.

The only effect on the binaries is 82 assert line numbers in video.cpp shifting
by four and one in jascreens.cpp shifting by one. No object file's section
sizes change.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Ja2/jascreens.cpp

@@ -36,7 +36,6 @@
 #include "sgp_logger.h"
 #include <language.hpp>
 
-#define _UNICODE
 // Networking Stuff
 #ifdef NETWORKED
 

sgp/video.cpp

@@ -22,10 +22,6 @@
 #include "Text.h"
 
 
-#ifndef _MT
-#define _MT
-#endif
-
 extern int iScreenMode;
 
 ///////////////////////////////////////////////////////////////////////////////////////////////////