lua: Use a lua_slice_state instead of a from_lua_visitor
lua: Use a lua_slice_state instead of a from_lua_visitor

A few places were using a from_lua_visitor only to access the
lua_slice_state member variable.

This is just a simplification. No functionality changed.

Signed-off-by: Rafael Ávila de Espíndola <1975039f9046bf513b77c0c5639a0efc25f00e7f@scylladb.com>

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