mdbx: reorganize internal includes.

mdbx.h

@@ -88,7 +88,6 @@ OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 
 /* *INDENT-OFF* */
 /* clang-format off */
-
 /**
  \file mdbx.h
  \brief The libmdbx C API header file
@@ -171,7 +170,6 @@ as a duplicates or as like a multiple values corresponds to keys.
  \defgroup c_rqest Range query estimation
  \defgroup c_extra Extra operations
 */
-
 /* *INDENT-ON* */
 /* clang-format on */