[test] Temporarily disable test IRGen/witness_method.sil.

Author: Greg Parker

test/IRGen/witness_method.sil

@@ -1,5 +1,8 @@
 // RUN: %target-swift-frontend -Xllvm -new-mangling-for-tests -assume-parsing-unqualified-ownership-sil %s -emit-ir | %FileCheck --check-prefix=CHECK --check-prefix=CHECK-%target-cpu %s
 
+// FIXME: rdar://30765842 redundant call to protocol witness table accessor
+// REQUIRES: rdar30765842
+
 // REQUIRES: CPU=i386 || CPU=x86_64
 
 sil_stage canonical