qa/suites/krbd: move "layering only" coverage to fsx

It makes much more sense there since it's where we actually create
clones and flatten them a lot.

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

Author: idryomov

qa/suites/krbd/fsx/features/no-deep-flatten.yaml

@@ -0,0 +1,6 @@
+overrides:
+  ceph:
+    conf:
+      client:
+        # layering
+        rbd default features: 1

qa/suites/krbd/unmap/conf.yaml

@@ -3,5 +3,3 @@ overrides:
     conf:
       global:
         mon warn on pool no app: false
-      client:
-        rbd default features: 1 # pre-single-major is v3.13, so layering only