LICENSE: restore LICENSE

I guess https://go-review.googlesource.com/c/vscode-go/+/255965
triggered unintended merge of release-branch only commits
(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 <[email protected]>
Run-TryBot: Hyang-Ah Hana Kim <[email protected]>
TryBot-Result: kokoro <[email protected]>
Reviewed-by: Suzy Mueller <[email protected]>

Author: hyangah