core/lazy_map+set: avoid calling delete when given key is not present

.changelog/unreleased/bug-fixes/1984-rm-redundant-writes.md

@@ -0,0 +1,4 @@
+- Avoid redundant storage deletions in lazy collections that would incur
+  extra gas cause and appear in transaction result as changed keys even if not
+  changed occurred. This may have caused PoS transactions to run out of gas.
+  ([\#1984](https://github.com/anoma/namada/pull/1984))

core/src/ledger/storage_api/collections/lazy_map.rs

@@ -482,16 +482,18 @@ where
         Ok(previous)
     }
 
-    /// Removes a key from the map, returning the value at the key if the key
-    /// was previously in the map.
+    /// Removes a key from the map if it's present, returning the value at the
+    /// key if the key was previously in the map.
     pub fn remove<S>(&self, storage: &mut S, key: &K) -> Result<Option<V>>
     where
         S: StorageWrite + StorageRead,
     {
         let value = self.get(storage, key)?;
 
-        let data_key = self.get_data_key(key);
-        storage.delete(&data_key)?;
+        if value.is_some() {
+            let data_key = self.get_data_key(key);
+            storage.delete(&data_key)?;
+        }
 
         Ok(value)
     }

core/src/ledger/storage_api/collections/lazy_set.rs

@@ -183,16 +183,18 @@ where
         storage.write(&key, ())
     }
 
-    /// Removes a key from the set, returning `true` if the key
+    /// Removes a key from the set if it's present, returning `true` if the key
     /// was in the set.
     pub fn remove<S>(&self, storage: &mut S, key: &K) -> Result<bool>
     where
         S: StorageWrite + StorageRead,
     {
         let present = self.contains(storage, key)?;
 
-        let key = self.get_key(key);
-        storage.delete(&key)?;
+        if present {
+            let key = self.get_key(key);
+            storage.delete(&key)?;
+        }
 
         Ok(present)
     }