internal/impl: change Go representation of extension lists to []T

Change-Id: Iebcefe0330c8f858c7735f9362abfd87043ee39d
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/192458
Reviewed-by: Joe Tsai <joetsai@google.com>
diff --git a/internal/impl/extension.go b/internal/impl/extension.go
index 8192223..c64f8f5 100644
--- a/internal/impl/extension.go
+++ b/internal/impl/extension.go
@@ -151,7 +151,7 @@
 		xi.initFromLegacy()
 	} else if xi.desc.Cardinality() == pref.Repeated {
 		// Cardinality is initialized lazily, so we defer consulting it until here.
-		xi.goType = reflect.PtrTo(reflect.SliceOf(xi.goType))
+		xi.goType = reflect.SliceOf(xi.goType)
 	}
 	xi.conv = NewConverter(xi.goType, xi.desc)
 	xi.tdesc.ExtensionDescriptor = xi.desc