s3: route non-conditional suspended DELETE off the DLM

A suspended DELETE removes the null version (the main object entry) and adds a
delete marker. Now that suspended PUT routes on the object key, a DELETE left on
the distributed lock wouldn't serialize against it (the per-path entry lock and
the distributed lock are independent). Route it on the object key too.

FinalizeVersionedWrite gains an optional delete_path it removes under the same
lock before flipping the pointer, so "delete null + add marker" is one atomic
step on the owner. createDeleteMarker threads it through (empty for the
versioning-enabled marker path). The DeleteObjectHandler routes a no-versionId
suspended delete when there is no If-Match — that condition targets the main
object, not the .versions pointer the op evaluates, so a conditional suspended
delete stays on the lock path. Object-lock can't apply (it requires versioning
enabled, never suspended).

other/java/client/src/main/proto/filer.proto

@@ -292,6 +292,7 @@ message UpdateEntryResponse {
 // from set_extended[prior_latest_key].
 message FinalizeVersionedWriteRequest {
     string lock_key = 13;                // object path; the per-path lock all of this object's writes share
+    string delete_path = 14;             // optional entry to delete under the lock first (suspended delete: the null version)
     string versions_dir = 1;             // full path of <object>/.versions
     map<string, bytes> set_extended = 3; // merge into the .versions directory entry
     repeated string delete_extended = 4; // remove from the .versions directory entry