thrift: Use database::find_schema directly
thrift: Use database::find_schema directly

This patch changes lookup_schema() so it directly calls
database::find_schema() instead of going through
database::find_column_family(). It also drops conversion of the
no_such_column_family exeption, as that is already handled at a higher
layer.

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

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