[bindings][ocaml] Remove a reference to the deleted function llvm_x86_mmx_type

The function was removed in dfeb399.

This change fixes the build for OCaml bindings and tests.

Author: gribozavr

llvm/bindings/ocaml/llvm/llvm.ml

@@ -519,7 +519,6 @@ external vector_size : lltype -> int = "llvm_vector_size"
 (*--... Operations on other types ..........................................--*)
 external void_type : llcontext -> lltype = "llvm_void_type"
 external label_type : llcontext -> lltype = "llvm_label_type"
-external x86_mmx_type : llcontext -> lltype = "llvm_x86_mmx_type"
 external type_by_name : llmodule -> string -> lltype option = "llvm_type_by_name"
 
 external classify_value : llvalue -> ValueKind.t = "llvm_classify_value"