all: update the tsd.System constructor name (#15372)

Replace NewSystemWithEventBus with plain NewSystem, and update all usage.
See https://github.com/tailscale/tailscale/pull/15355#discussion_r2003910766

Updates #15160

Change-Id: I64d337f09576b41d9ad78eba301a74b9a9d6ebf4
Signed-off-by: M. J. Fromberger <fromberger@tailscale.com>
This commit is contained in:
Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f