[dev.typeparams] cmd/compile: re-enable internal/types2 test

[dev.typeparams] cmd/compile: re-enable internal/types2 test

CL 279531 disabled these because they were causing
trouble with the automation for the big move.
The big move is over. Reenable them.

Change-Id: I2b06f619a114ebcc9b9af73ce0d5b68ebaeaac03
Reviewed-on: https://go-review.googlesource.com/c/go/+/279993
Trust: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>