tt: Fixup tt build for new includes locations

Some files were trying to access the global includes directy in the
build area with things like #include <api/c/tt_c.h>, which is now
wrong.  Se we fix all of those up.  tt_c.h and tttk.h are now global,
so we no longer need to root around various build dirs to find them.

TT builds again.

cde/lib/tt/bin/shell/remover.C

@@ -46,7 +46,7 @@
 #include <errno.h>
 #include <sys/stat.h>
 #include <sys/wait.h>
-#include "api/c/tt_c.h"
+#include "Tt/tt_c.h"
 #include "util/tt_path.h"
 #include "util/tt_gettext.h"
 #include "util/copyright.h"