LICENSE: restore LICENSE

I guess https://go-review.googlesource.com/c/vscode-go/+/255965
triggered unintended merge of release-branch only commits
(golang@ed434b2)

This reverts the change in the LICENSE file. We include the full LICENSE
only in the released product. This should be identical with the version at
https://github.com/golang/vscode-go/blob/85e647e938c2e5337c2ed9464853fc39b6eded99/LICENSE

I attempted to revert the merge CL, but it seems too dangerous and
I am afraid that that will mess up the history further.

Change-Id: I6d627c7a541bc513daeda5a49d6f43913bbbc41c
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/258341
Trust: Hyang-Ah Hana Kim <hyangah@gmail.com>
Run-TryBot: Hyang-Ah Hana Kim <hyangah@gmail.com>
TryBot-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Suzy Mueller <suzmue@golang.org>