Delete the rules_go load rule if it's not needed

[ixdy]

If you try generating vendor/BUILD from scratch with VendorMultipleBuildFiles enabled, we add a useless load line:

load("@io_bazel_rules_go//go:def.bzl")

Simplest fix is to automatically remove this line in reconciliation when we don't need it.

x-ref kubernetes/kubernetes#41287 (comment).

[spxtr]

gazel is certainly not the most beautiful code to work with here...

How confident are you that this works as you expect?

[ixdy]

I've manually tested this and verified that it works.

If I run gazel on kubernetes/test-infra or kubernetes/kubernetes, no files change.

If I remove vendor/BUILD from either, it regenerates it correctly (without the useless load line in multi-vendor).

If I add a rules_go load line to a BUILD file with no go rules (e.g. jenkins/BUILD), it removes it as expected.

[spxtr]

That's sufficient for me.

LGTM