Revert "towards moving config into context"

This reverts commit 7427716ea8.

github/hosts.go

@@ -0,0 +1,64 @@
+package github
+
+import (
+	"fmt"
+	"net/url"
+	"os"
+	"strings"
+
+	"github.com/github/gh-cli/git"
+)
+
+var (
+	GitHubHostEnv = os.Getenv("GITHUB_HOST")
+	cachedHosts   []string
+)
+
+type GithubHostError struct {
+	url *url.URL
+}
+
+func (e *GithubHostError) Error() string {
+	return fmt.Sprintf("Invalid GitHub URL: %s", e.url)
+}
+
+func KnownGitHubHostsInclude(host string) bool {
+	for _, hh := range knownGitHubHosts() {
+		if hh == host {
+			return true
+		}
+	}
+
+	return false
+}
+
+func knownGitHubHosts() []string {
+	if cachedHosts != nil {
+		return cachedHosts
+	}
+
+	hosts := []string{}
+	defaultHost := DefaultGitHubHost()
+	hosts = append(hosts, defaultHost)
+	hosts = append(hosts, "ssh.github.com")
+
+	ghHosts, _ := git.ConfigAll("hub.host")
+	for _, ghHost := range ghHosts {
+		ghHost = strings.TrimSpace(ghHost)
+		if ghHost != "" {
+			hosts = append(hosts, ghHost)
+		}
+	}
+
+	cachedHosts = hosts
+	return hosts
+}
+
+func DefaultGitHubHost() string {
+	defaultHost := GitHubHostEnv
+	if defaultHost == "" {
+		defaultHost = GitHubHost
+	}
+
+	return defaultHost
+}