Remove duplicate package description.

[AlekSi]

To prevent it from appearing twice on
https://pkg.go.dev/github.com/sethvargo/go-githubactions

[AlekSi]

It already present in the other file:

go-githubactions/actions.go

Lines 15 to 18 in a712c2e

	// Package githubactions provides an SDK for authoring GitHub Actions in Go. It
	// has no external dependencies and provides a Go-like interface for interacting
	// with GitHub Actions' build system.
	package githubactions

[sethvargo]

Thanks!