[AArch64] Fix a warning

This patch fixes:

  lib/Target/AArch64/AArch64GenPostLegalizeGILowering.inc:506:14:
  error: unused variable 'GIMatchData_matchinfo'
  [-Werror,-Wunused-variable]

Author: kazutakahirata

llvm/lib/Target/AArch64/AArch64Combine.td

@@ -223,7 +223,7 @@ def build_vector_to_dup : GICombineRule<
 >;
 
 def build_vector_to_vector_insert : GICombineRule<
-  (defs root:$root, register_matchinfo:$matchinfo),
+  (defs root:$root),
   (match (G_BUILD_VECTOR $dst, GIVariadic<>:$unused):$root,
           [{ return matchLowerBuildToInsertVecElt(*${root}, MRI); }]),
   (apply [{ applyLowerBuildToInsertVecElt(*${root}, MRI, B); }])