This makes it so that 'go install golang.org/x/tools/go/pointer@latest'
will continue to work. ('go install pkg@version' does not allow
replace directives.)

Updates golang/go#59676

Change-Id: I7dcb95a5730bd68d42a5873f9f9cec6bef773205
Reviewed-on: https://go-review.googlesource.com/c/tools/+/499756
gopls-CI: kokoro <[email protected]>
Run-TryBot: Alan Donovan <[email protected]>
Reviewed-by: Robert Findley <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>