OvmfPkg: Remove duplicated library classes in dxe drivers section in DSC

OvmfPkg: Remove duplicated library classes in dxe drivers section in DSC

NetLib,IpIoLib,UdpIoLib and DpcLib already exist in [LibraryClasses].
So the ones in [LibraryClasses.common.DXE_DRIVER] are duplicated,
which should be removed.

Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Anthony Perard <anthony.perard@citrix.com>
Cc: Julien Grall <julien.grall@linaro.org>
Signed-off-by: Shenglei Zhang <shenglei.zhang@intel.com>
Message-Id: <20190515072419.23792-1-shenglei.zhang@intel.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=1293
[lersek@redhat.com: add TianoCore BZ reference]
Reviewed-by: Laszlo Ersek <lersek@redhat.com>