UnXFAIL untyped_var test after spirv-tools update (#2748)

With the latest release of spirv-tools (1.3.296) this test now passes.

Original commit:
KhronosGroup/SPIRV-LLVM-Translator@a217f5e3449eaa8

Author: svenvh

llvm-spirv/test/extensions/KHR/SPV_KHR_untyped_pointers/untyped_var.spvasm

@@ -1,6 +1,3 @@
-; TODO: enable back once spirv-tools are updated.
-; XFAIL: *
-
 ; REQUIRES: spirv-as
 ; RUN: spirv-as --target-env spv1.6 -o %t.spv %s
 ; RUN: spirv-val %t.spv