doc: remove rebase-snap instructions from documentation

The rebase-snap tool is deprecated and snapshot-editor should be used.
Since the two ways of merging snapshot files are completely equivalent,
let's remove the rebase-snap instructions and only keep the
snapshot-editor ones, to avoid people using deprecated tools.

Signed-off-by: Patrick Roy <[email protected]>

Author: roypat

docs/snapshotting/snapshot-support.md

@@ -216,16 +216,8 @@ call and the layer as a memory file created by a subsequent `/snapshot/create`
 API call. The order in which the snapshots were created matters and they should
 be merged in the same order in which they were created. To merge a `diff`
 snapshot memory file on top of a base, users should copy its content over the
-base. This can be done using the `rebase-snap` (deprecated) or `snapshot-editor`
-tools provided with the firecracker release:
-
-`rebase-snap` (deprecated) example:
-
-```bash
-rebase-snap --base-file path/to/base --diff-file path/to/layer
-```
-
-`snapshot-editor` example:
+base. This can be done using the `snapshot-editor` tools provided with the
+firecracker release:
 
 ```bash
 snapshot-editor edit-memory rebase \