control: HSFETCH does not support v3 yet

The HSFETCH command was not implemented for v3 with prop284 work because of
some engineering complexity and lack of use case.

See ticket #20699 for the rationale.

Signed-off-by: David Goulet <dgoulet@torproject.org>

control-spec.txt

@@ -1480,14 +1480,13 @@
     "HSFETCH" SP (HSAddress / "v" Version "-" DescId)
               *[SP "SERVER=" Server] CRLF
 
-    HSAddress = (16*Base32Character / 56*Base32Character)
-    Version = "2" / "3"
-    DescId = (32*Base32Character / 32*Base64Character)
+    HSAddress = 16*Base32Character
+    Version = "2"
+    DescId = 32*Base32Character
     Server = LongName
 
   This command launches hidden service descriptor fetch(es) for the given
-  HSAddress or DescId. For v3, "DescId" is the descriptor blinded key used as
-  an index to query the directory. It can only be used with "Version=3".
+  HSAddress or DescId.
 
   If a DescId is specified, at least one Server MUST also be provided,
   otherwise a 512 error is returned. If no DescId and Server(s) are specified,
@@ -1515,7 +1514,6 @@
      S: 250 OK
 
   [HSFETCH was added in Tor 0.2.7.1-alpha]
-  [HS v3 support added 0.3.3.1-alpha]
 
 3.27. ADD_ONION