Remove `<adiar/file.h>` and `<adiar/map_pair.h>`

[SSoelvsten]

With all the breaking changes in #147 , #452, and #532 done, we have made the use of adiar::file and adiar::shared_file completely unusable in the public API. Hence, we may as well remove it.

• Remove <adiar/file.h>
  • Remove dependency on <adiar/file.h> in <adiar/bdd.h>
  • Remove dependency on <adiar/file.h> in <adiar/zdd.h>
  • Clean up unit tests that needed to use internal::file_stream<...> and internal::file_writer<...> to resolve ambiguity.
• Remove <adiar/map_pair.h>
  • Remove dependency on <adiar/map_pair.h> in <adiar/bdd.h>
  • Remove unit tests for <adiar/map_pair.h>.