Remove remaining Guava dependencies from SnapshotDiffApplier

- Replace Sets.difference() with standard Java stream operations
- Remove unused Objects import
- Use streams with filter/collect instead of Guava Sets utility methods
- Reduces external dependencies and aligns with PR1 implementation

Author: cbb330

iceberg/openhouse/internalcatalog/src/main/java/com/linkedin/openhouse/internal/catalog/SnapshotDiffApplier.java

@@ -18,7 +18,6 @@
 import org.apache.iceberg.SnapshotRef;
 import org.apache.iceberg.SnapshotSummary;
 import org.apache.iceberg.TableMetadata;
-import org.apache.iceberg.relocated.com.google.common.base.Objects;
 
 /**
  * Service responsible for applying snapshot changes to Iceberg table metadata.
@@ -166,8 +165,14 @@ private class SnapshotDiff {
           deletedSnapshots.stream().map(Snapshot::snapshotId).collect(Collectors.toSet());
       this.newRegularSnapshots =
           regularSnapshots.stream().filter(newSnapshots::contains).collect(Collectors.toList());
-      this.staleRefs = Sets.difference(existingRefs.keySet(), providedRefs.keySet());
-      this.existingAfterDeletionIds = Sets.difference(existingSnapshotByIds.keySet(), deletedIds);
+      this.staleRefs =
+          existingRefs.keySet().stream()
+              .filter(key -> !providedRefs.containsKey(key))
+              .collect(Collectors.toSet());
+      this.existingAfterDeletionIds =
+          existingSnapshotByIds.keySet().stream()
+              .filter(id -> !deletedIds.contains(id))
+              .collect(Collectors.toSet());
       this.unreferencedNewSnapshots =
           providedSnapshots.stream()
               .filter(