Remove deprecated headers in metafunctions.hpp (Issue #106)

There are three headers included in this file which are deprecated.

They each pull in a header that is already included.
They each define a deprecated struct (range_result_iterator, range_const_reverse_iterator, and range_reverse_result_iterator, respectively. However:
boost itself does not rely on these structs being defined via inclusion of this header
users of boost can simply add a #include of the required file, or (better) change their usage to avoid the deprecated structs.

boostorg / range