thrift: Introduce with_schema function
thrift: Introduce with_schema function

This is a wrapper around with_cob, which fetches a schema and forwards
it to a supplied function.

The patch also removes superfluous return instructions.

Signed-off-by: Duarte Nunes <a60e8b7496f7715d71354fe4c06dd24017025bf1@scylladb.com>

scylladb/scylla,duarten/scylla,kjniemi/scylla,avikivity/scylla,duarten/scylla,scylladb/scylla,kjniemi/scylla,raphaelsc/scylla,avikivity/scylla,scylladb/scylla,raphaelsc/scylla,raphaelsc/scylla,scylladb/scylla,duarten/scylla,avikivity/scylla,kjniemi/scylla