doc: move Go 1.19 release notes to x/website
doc: move Go 1.19 release notes to x/website

Now that the development of the Go 1.19 release is almost done, its
release notes are moved to their eventual long-term home in x/website
in CL 420417. Delete the initial development copy here.

For golang/go#51400.

Change-Id: I741285555af28ce9a64e7f8d2b9fe2a0f3e13c26
Reviewed-on: https://go-review.googlesource.com/c/go/+/420418
Reviewed-by: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@google.com>
Run-TryBot: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@golang.org>
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Cherry Mui <d62e63aa42ce272d7b6a5055d97e942b33a34679@google.com>

golang/go,golang/go,golang/go,golang/go,golang/go,golang/go,golang/go,golang/go