It seems that the following functions are never used, delete them:
* `function::has_reference_to`
* `functions::get_overload_count`
* `to_identifiers` in column_identifier.hh
* `single_column_relation::get_map_key`
Tests: unit(dev, debug)
Signed-off-by: Pavel Solodovnikov <pa.solodovnikov@scylladb.com>
Message-Id: <20200606115149.1770453-1-pa.solodovnikov@scylladb.com>