v2: remove v2 implementation and point people at tailscale.com/client/tailscale/v2

Updates tailscale/corp#22748

Signed-off-by: Percy Wegmann <[email protected]>

Author: oxtoacart

README.md

@@ -1,14 +1,11 @@
 # tailscale-client-go
 
-A Go client implementation for the [Tailscale API](https://tailscale.com/api).
-
-## Current Version
+> [!IMPORTANT]
+> This implementation is no longer maintained. The replacement is available at [tailscale-client-go-v2](https://github.com/tailscale/tailscale-client-go-v2).
 
- * [V2](https://github.com/tailscale/tailscale-client-go/tree/main/v2#readme): `import "github.com/tailscale/tailscale-client-go/v2"`
-
-   [![Go Reference](https://pkg.go.dev/badge/github.com/tailscale/tailscale-client-go.svg)](https://pkg.go.dev/github.com/tailscale/tailscale-client-go/v2)
+A Go client implementation for the [Tailscale API](https://tailscale.com/api).
 
-## Old versions
+## Old version
 
 * V1: `import "github.com/tailscale/tailscale-client-go"`