Maintainers.txt: Remove unused OvmfPkg Confidential Computing path

The following commit removed PlatformBootManagerLibGub from
OvmfPkg.  Update Maintainers.txt to remove reference to
deleted directory.

tianocore/edk2@6fb2760

Cc: Andrew Fish <[email protected]>
Cc: Leif Lindholm <[email protected]>
Cc: Erdem Aktas <[email protected]>
Cc: Jiewen Yao <[email protected]>
Cc: Min Xu <[email protected]>
Cc: Tom Lendacky <[email protected]>
Cc: Michael Roth <[email protected]>
Signed-off-by: Michael D Kinney <[email protected]>
Acked-by: Jiewen Yao <[email protected]>
Acked-by: Gerd Hoffmann <[email protected]>
Reviewed-by: Leif Lindholm <[email protected]>

Maintainers.txt

@@ -497,7 +497,6 @@ F: OvmfPkg/Include/Guid/ConfidentialComputingSecret.h
 F: OvmfPkg/Include/Library/MemEncryptSevLib.h
 F: OvmfPkg/IoMmuDxe/CcIoMmu.*
 F: OvmfPkg/Library/BaseMemEncryptSevLib/
-F: OvmfPkg/Library/PlatformBootManagerLibGrub/
 F: OvmfPkg/Library/CcExitLib/
 F: OvmfPkg/PlatformPei/AmdSev.c
 F: OvmfPkg/ResetVector/