delete the stack tracer that never captured a frame

ENABLE_STACK_TRACE has been 0 for as long as the file has been here, so
StackTrace's constructor captured nothing and every line it ever wrote to
stack_trace.log was a bare message with an empty frame list behind it. The
DbgHelp singleton underneath it resolved symbols for that empty list, and
the game linked dbghelp.lib to do it.

The crash reports cover what this was meant to cover, and the VFS errors
that were its only real content are already in vfs.log and game_log.log.
Drop the tracer, the log, and the dbghelp dependency.

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

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

sgp/DEBUG.cpp

@@ -397,8 +397,6 @@ void _FailMessage(const char* message, unsigned lineNum, const char * functionNa
 	// everything below it (a stack walk, a save, a screen) can die trying.
 	sgp::raiseAssertException(lineNum, sourceFileName, message);
 
-	sgp::dumpStackTrace(message);
-
 	mprintf( 10, 10, L"%s: %s %s", pMessageStrings[ MSG_VERSION ], zProductLabel, zBuildInformation );
 
 	std::stringstream basicInformation;