Remove unhelpful link to very old doc.

There's nothing useful in that doc that isn't already here.

PiperOrigin-RevId: 678807994
Change-Id: I50d345d84173d732fd41c1bdf1f6fc1aec42c5d8
1 file changed
tree: 668ee617633f99599da07e6eedd2b62fc25fc546
  1. api-guidelines/