_recv_into() is not used anymore

[vladak]

This change removes _recv_into(). It was initially introduced in 8492a58f88465148268546fd58712c41208dee6c, then actually used in 2ae61a459dd2842981a15b63f0e60c0a84646749 and then the call was removed in ea966339379c8081dba94c95bd1f286dfe4dcca1.