tboot: remove maintainers and declare orphaned

Gang Wei Intel email address has been bouncing for some time now, and
the other maintainer is non-responsive to patches [0], so remove
maintainers and declare INTEL(R) TRUSTED EXECUTION TECHNOLOGY (TXT)
orphaned.

[0] https://lists.xenproject.org/archives/html/xen-devel/2019-05/msg00563.html

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>

MAINTAINERS

@@ -240,9 +240,7 @@ S:	Maintained
 F:	tools/golang
 
 INTEL(R) TRUSTED EXECUTION TECHNOLOGY (TXT)
-M:	Gang Wei <gang.wei@intel.com>
-M:	Shane Wang <shane.wang@intel.com>
-S:	Supported
+S:	Orphaned
 F:	xen/arch/x86/tboot.c
 F:	xen/include/asm-x86/tboot.h