go.mod: rm toolchain

This was added by dependabot in commit 0b53626. Seems there is a bug
about it: dependabot/dependabot-core#11933.

Having "toolchain" means instead of using installed go version to
build/test, the version specified in toolchain is [downloaded and] used,
which might not be what we actually want.

For more details on toolchain directive, see
https://go.dev/doc/toolchain.

Signed-off-by: Kir Kolyshkin <[email protected]>

Author: kolyshkin

go.mod

@@ -2,8 +2,6 @@ module github.com/opencontainers/runc
 
 go 1.23.0
 
-toolchain go1.24.1
-
 require (
 	github.com/checkpoint-restore/go-criu/v7 v7.2.0
 	github.com/containerd/console v1.0.4