Make host_timestamp() abstract (#457)

* make host_timestamp abstract

* changelog

* changelog

Author: plafer

.changelog/unreleased/breaking-changes/418-host-timestamp.md

@@ -0,0 +1,3 @@
+- Make ValidationContext::host_timestamp() abstract and remove
+  ValidationContext::pending_host_consensus_state()
+  ([#418](https://github.com/cosmos/ibc-rs/issues/418))

crates/ibc/src/core/context.rs

@@ -269,15 +269,7 @@ pub trait ValidationContext: Router {
     fn host_height(&self) -> Result<Height, ContextError>;
 
     /// Returns the current timestamp of the local chain.
-    fn host_timestamp(&self) -> Result<Timestamp, ContextError> {
-        let pending_consensus_state = self
-            .pending_host_consensus_state()
-            .expect("host must have pending consensus state");
-        Ok(pending_consensus_state.timestamp())
-    }
-
-    /// Returns the pending `ConsensusState` of the host (local) chain.
-    fn pending_host_consensus_state(&self) -> Result<Box<dyn ConsensusState>, ContextError>;
+    fn host_timestamp(&self) -> Result<Timestamp, ContextError>;
 
     /// Returns the `ConsensusState` of the host (local) chain at a specific height.
     fn host_consensus_state(

crates/ibc/src/mock/context.rs

@@ -824,10 +824,6 @@ impl ValidationContext for MockContext {
             .unwrap())
     }
 
-    fn pending_host_consensus_state(&self) -> Result<Box<dyn ConsensusState>, ContextError> {
-        Err(ClientError::ImplementationSpecific.into())
-    }
-
     fn host_consensus_state(
         &self,
         height: &Height,