Consistent capitalization

The release binary was called Jet2.exe (according to the XBE header), so
they were apparently capitalizing file names.  This was already
reflected in objects.csv, but not the source files.

src/jet2.cpp

@@ -1,15 +0,0 @@
-#include "core.hpp"
-
-
-// Address: 0x0022FCE0
-Game * g_game;
-
-
-// Address: 0x0006F9E0
-// Matching: no
-void main(void) {
-    g_game = new Game(NULL, 0);
-    g_game->initExecRootObj();
-    g_game->mainLoop();
-    delete g_game;
-}