go.mod: remove toolchain line (#31057)

We have our own system for downloading the toolchain, and really don't
want Go's to get in the way of that. We may switch to Go's builtin
toolchain support, but not now.

go.mod

@@ -2,8 +2,6 @@ module github.com/ethereum/go-ethereum
 
 go 1.22
 
-toolchain go1.22.0
-
 require (
 	github.com/Azure/azure-sdk-for-go/sdk/storage/azblob v1.2.0
 	github.com/Microsoft/go-winio v0.6.2