rpc: turn off getStakeActivation epoch parameter (#33156)

* Return error on past-epoch parameter

* Update docs

Author: Tyera

docs/src/api/methods/_getStakeActivation.mdx

@@ -41,6 +41,7 @@ Configuration object containing the following fields:
 <Field name="epoch" type="u64" optional={true}>
   epoch for which to calculate activation details. If parameter not provided,
   defaults to current epoch.
+  **DEPRECATED**, inputs other than the current epoch return an error.
 </Field>
 
 </Parameter>

rpc/src/rpc.rs

@@ -1719,14 +1719,10 @@ impl JsonRpcRequestProcessor {
             min_context_slot: config.min_context_slot,
         })?;
         let epoch = config.epoch.unwrap_or_else(|| bank.epoch());
-        if bank.epoch().saturating_sub(epoch) > solana_sdk::stake_history::MAX_ENTRIES as u64 {
+        if epoch != bank.epoch() {
             return Err(Error::invalid_params(format!(
-                "Invalid param: epoch {epoch:?} is too far in the past"
-            )));
-        }
-        if epoch > bank.epoch() {
-            return Err(Error::invalid_params(format!(
-                "Invalid param: epoch {epoch:?} has not yet started"
+                "Invalid param: epoch {epoch:?}. Only the current epoch ({:?}) is supported",
+                bank.epoch()
             )));
         }