cass_types: remove consistency conversion impls

`impl TryFrom<CassConsistency> for (Serial)Consistency` are removed,
as they are:
- Not used anymore in the codebase.
- Prone to misuse, because there are two different semantics of such
  conversion:
  1. For statement/batch/exec_profile, where `CASS_CONSISTENCY_UNKNOWN`
     is allowed and must be handled.
  2. For cluster, where `CASS_CONSISTENCY_UNKNOWN` is not allowed,
     and must result in an error.

As a bug-resitant alternative, the `MaybeUnsetConfig` type is promoted.

Author: wprzytula

scylla-rust-wrapper/src/cass_types.rs

@@ -3,10 +3,8 @@ use crate::cass_error::CassError;
 use crate::types::*;
 use scylla::cluster::metadata::{CollectionType, NativeType};
 use scylla::frame::response::result::ColumnType;
-use scylla::frame::types::{Consistency, SerialConsistency};
 use scylla::statement::batch::BatchType;
 use std::cell::UnsafeCell;
-use std::convert::TryFrom;
 use std::os::raw::c_char;
 use std::sync::Arc;
 
@@ -894,39 +892,6 @@ pub unsafe extern "C" fn cass_data_type_add_sub_value_type_by_name_n(
     }
 }
 
-impl TryFrom<CassConsistency> for Consistency {
-    type Error = ();
-
-    fn try_from(c: CassConsistency) -> Result<Consistency, Self::Error> {
-        match c {
-            CassConsistency::CASS_CONSISTENCY_ANY => Ok(Consistency::Any),
-            CassConsistency::CASS_CONSISTENCY_ONE => Ok(Consistency::One),
-            CassConsistency::CASS_CONSISTENCY_TWO => Ok(Consistency::Two),
-            CassConsistency::CASS_CONSISTENCY_THREE => Ok(Consistency::Three),
-            CassConsistency::CASS_CONSISTENCY_QUORUM => Ok(Consistency::Quorum),
-            CassConsistency::CASS_CONSISTENCY_ALL => Ok(Consistency::All),
-            CassConsistency::CASS_CONSISTENCY_LOCAL_QUORUM => Ok(Consistency::LocalQuorum),
-            CassConsistency::CASS_CONSISTENCY_EACH_QUORUM => Ok(Consistency::EachQuorum),
-            CassConsistency::CASS_CONSISTENCY_LOCAL_ONE => Ok(Consistency::LocalOne),
-            CassConsistency::CASS_CONSISTENCY_LOCAL_SERIAL => Ok(Consistency::LocalSerial),
-            CassConsistency::CASS_CONSISTENCY_SERIAL => Ok(Consistency::Serial),
-            _ => Err(()),
-        }
-    }
-}
-
-impl TryFrom<CassConsistency> for SerialConsistency {
-    type Error = ();
-
-    fn try_from(serial: CassConsistency) -> Result<SerialConsistency, Self::Error> {
-        match serial {
-            CassConsistency::CASS_CONSISTENCY_SERIAL => Ok(SerialConsistency::Serial),
-            CassConsistency::CASS_CONSISTENCY_LOCAL_SERIAL => Ok(SerialConsistency::LocalSerial),
-            _ => Err(()),
-        }
-    }
-}
-
 pub(crate) fn make_batch_type(type_: CassBatchType) -> Option<BatchType> {
     match type_ {
         CassBatchType::CASS_BATCH_TYPE_LOGGED => Some(BatchType::Logged),