[WebAssembly] Remove IIT_EXNREF

This was added in #93586 but caused a compilation warning and is not
used anyway.

Author: aheejin

llvm/include/llvm/IR/Intrinsics.td

@@ -316,7 +316,6 @@ def IIT_PPCF128 : IIT_VT<ppcf128, 52>;
 def IIT_V3 : IIT_Vec<3, 53>;
 def IIT_EXTERNREF : IIT_VT<externref, 54>;
 def IIT_FUNCREF : IIT_VT<funcref, 55>;
-def IIT_EXNREF: IIT_VT<exnref, 56>;
 def IIT_I2 : IIT_Int<2, 57>;
 def IIT_I4 : IIT_Int<4, 58>;
 def IIT_AARCH64_SVCOUNT : IIT_VT<aarch64svcount, 59>;