Revert "Add a module for stl_iterator_base_funcs.h avoiding merging issues for c++20"

This reverts commit a4c07502.

While this itself might not cause build issues, the related commit 90ffa89a does;
handle them together.

interpreter/cling/include/cling/std.modulemap

@@ -459,10 +459,6 @@ module "std" [system] {
     export *
     header "bits/stl_iterator.h"
   }
-  module "bits/stl_iterator_base_funcs.h" {
-    export *
-    header "bits/stl_iterator_base_funcs.h"
-  }
   module "bits/stl_iterator_base_types.h" {
     export *
     export bits_stl_algobase_h