Changes

Remove Is_in_code_area and registration of code in page table (#9697)

Previously, code areas from native-code DLLs were registered in the page
table and could be queried with the Is_in_code_area macros.

Following commit e4bf109d1 (PR#9682), the runtime system no longer
queries the page table for code areas (it uses the table of code fragments
instead).

A grep through OPAM package sources shows no uses of Is_in_code_area macro
or the In_code_area flag for pages.

This commit simply removes the Is_in_code_area macro and the registration
of code areas in the page table.
 (commit: b18ac65)