Clear stages key in dvc.lock

This is so that future bricks do not bring in the unused stage.

dvc.lock

@@ -1,12 +1,2 @@
 schema: '2.0'
-stages:
-  1-stage:
-    cmd: Rscript stages/01-stage.R
-    deps:
-    - path: stages/01-stage.R
-      md5: c468dc14527e00c339f146e1dba2bd3b
-      size: 118
-    outs:
-    - path: data/mtcars.parquet
-      md5: 77cf29accf9535522fad7db1486eff9a
-      size: 6243
+stages: {}