go/internal/gcimporter: set iexportVersionGenerics to 2

Now that the standard library importer/exporter has been updated for a
while, we can set iexportVersionGenerics to its final value -- 2.

Fixes golang/go#47654

Change-Id: I27eca4cf2b82b7c09e2b6a754c6e5e5af71a7b29
Reviewed-on: https://go-review.googlesource.com/c/tools/+/377554
Trust: Robert Findley <[email protected]>
Run-TryBot: Robert Findley <[email protected]>
gopls-CI: kokoro <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Dan Scales <[email protected]>
Trust: Dan Scales <[email protected]>

go/internal/gcimporter/iimport.go

@@ -45,20 +45,11 @@ func (r *intReader) uint64() uint64 {
 }
 
 // Keep this in sync with constants in iexport.go.
-//
-// Temporarily, the x/tools importer accepts generic code at both version 1 and
-// 2. However, version 2 contains some breaking changes on top of version 1:
-//   - the 'implicit' bit is added to exported constraints
-//   - a 'kind' byte is added to constant values (not yet done)
-//
-// Once we've completed the bump to version 2 in the standard library, we'll
-// remove support for generics here at version 1.
 const (
-	iexportVersionGo1_11 = 0
-	iexportVersionPosCol = 1
-	iexportVersionGo1_18 = 2
-	// TODO: before release, change this back to 2.
-	iexportVersionGenerics = iexportVersionPosCol
+	iexportVersionGo1_11   = 0
+	iexportVersionPosCol   = 1
+	iexportVersionGo1_18   = 2
+	iexportVersionGenerics = 2
 )
 
 type ident struct {