internal/sync: move HashTrieMap from internal/concurrent
This change moves internal/concurrent.HashTrieMap from
internal/concurrent into internal/sync just to clean up the packages a
bit. This is all in anticipation of using HashTrieMap from the sync
package.
Change-Id: I18c007a301f83979d72f5d6bea600c42eaf2421e
Reviewed-on: https://go-review.googlesource.com/c/go/+/594058
Auto-Submit: Michael Knyszek <mknyszek@google.com> Reviewed-by: David Chase <drchase@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>