Remove redundant errMsg403NoSuchCosigner interpolated error string.

This interpolated string is a duplicate of a similar interpolated string
in `Http.Server.Error`.

lib/wallet/integration/src/Test/Integration/Framework/TestData.hs

@@ -89,7 +89,6 @@ module Test.Integration.Framework.TestData
     , errMsg403OutputTokenBundleSizeExceedsLimit
     , errMsg403OutputTokenQuantityExceedsLimit
     , errMsg403KeyAlreadyPresent
-    , errMsg403NoSuchCosigner
     , errMsg403CreateIllegal
     , errMsg400ScriptWrongCoeffcient
     , errMsg400ScriptIllFormed
@@ -583,15 +582,6 @@ errMsg403KeyAlreadyPresent cred = mconcat
     , "Please make sure to assign a different key to each cosigner."
     ]
 
-errMsg403NoSuchCosigner :: Text -> Int -> String
-errMsg403NoSuchCosigner cred cosigner = unwords
-    [ "It looks like you've tried to add a cosigner key to a"
-    , "shared wallet's"
-    , unpack cred
-    , "template for a non-existing cosigner index:"
-    , show cosigner
-    ]
-
 errMsg403CreateIllegal :: String
 errMsg403CreateIllegal = mconcat
     [ "It looks like you've tried to create a shared wallet with a template "