west blobs: fix subcmd help

Without this patch, "west blobs -h" says:

  {list,fetch,clean} Select the sub-command to execute. Sub-commands
  available: - list: list binary blobs - fetch: fetch and store binary
  blobs - clean: remove fetched binary blobs

With this patch:

  {list,fetch,clean}    sub-command to execute

Signed-off-by: Martí Bolívar <marti.bolivar@nordicsemi.no>

scripts/west_commands/blobs.py

@@ -65,12 +65,7 @@ class Blobs(WestCommand):
         # flags
         parser.add_argument('subcmd', nargs=1,
                             choices=['list', 'fetch', 'clean'],
-                            help='''Select the sub-command to execute.
-							Sub-commands available:
-                            - list: list binary blobs
-                            - fetch: fetch and store binary blobs
-                            - clean: remove fetched binary blobs
-                            ''')
+                            help='sub-command to execute')
 
         parser.add_argument('-f', '--format', default=default_fmt,
                             help='''Format string to use to list each blob;