Remove the replace directive and update x/tools.

For golang/go#54294

Change-Id: I20a0f7933313cda03ca6be07c45df97194215c79
Reviewed-on: https://go-review.googlesource.com/c/tools/+/421497
gopls-CI: kokoro <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Dylan Le <[email protected]>
Run-TryBot: Robert Findley <[email protected]>