core: remove unused variables in Shamir recovery

(cherry picked from commit 6c50b155de)

core/src/apps/management/recovery_device.py

@@ -76,7 +76,7 @@ async def recovery_device(ctx, msg):
         if remaining == 0:
             try:
                 secret = mnemonic_module.process_all(mnemonics)
-            except slip39.MnemonicError as e:
+            except slip39.MnemonicError:
                 raise wire.ProcessError("Mnemonic is not valid")
         # show a number of remaining mnemonics for SLIP39
         if secret is None and mnemonic_module == mnemonic.slip39:

core/src/trezor/crypto/slip39.py

@@ -594,13 +594,6 @@ def combine_mnemonics(mnemonics):
 
     for group_index, group in groups.items():
         if len(group[1]) != group[0]:
-            prefix = _group_prefix(
-                identifier,
-                iteration_exponent,
-                group_index,
-                group_threshold,
-                group_count,
-            )
             raise MnemonicError(
                 "Wrong number of mnemonics. Expected {} mnemonics, but {} were provided.".format(
                     group[0], len(group[1])