legacy_schema_migrator: Properly migrate non-UTF8 named columns
legacy_schema_migrator: Properly migrate non-UTF8 named columns

Currently migrator assumed all columns are utf8-named, which
doesn't have to be the case for static compact tables.

Refs #2597.

Due to #2573, we can assume that Scylla wasn't used with non-utf8
column names, and that old names are always in textual form.

avikivity/scylla,duarten/scylla,scylladb/scylla,duarten/scylla,scylladb/scylla,avikivity/scylla,scylladb/scylla,duarten/scylla,scylladb/scylla,avikivity/scylla