gopls/internal/lsp: switch default diff to "new"

As the next step in the diff migration, stop running both diffs by
default.

For golang/go#52967

Change-Id: I4b1a434d13f4349feabc5eb0daf3b9e8d56f99aa
Reviewed-on: https://go-review.googlesource.com/c/tools/+/520135
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Peter Weinberger <pjw@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
gopls-CI: kokoro <noreply+kokoro@google.com>
diff --git a/gopls/internal/lsp/source/options.go b/gopls/internal/lsp/source/options.go
index c2e3223..45899e6 100644
--- a/gopls/internal/lsp/source/options.go
+++ b/gopls/internal/lsp/source/options.go
@@ -171,7 +171,7 @@
 				CompletionDocumentation:     true,
 				DeepCompletion:              true,
 				ChattyDiagnostics:           true,
-				NewDiff:                     "both",
+				NewDiff:                     "new",
 				SubdirWatchPatterns:         SubdirWatchPatternsAuto,
 				ReportAnalysisProgressAfter: 5 * time.Second,
 			},
diff --git a/gopls/internal/lsp/tests/tests.go b/gopls/internal/lsp/tests/tests.go
index 9ab114e..65e9c0e 100644
--- a/gopls/internal/lsp/tests/tests.go
+++ b/gopls/internal/lsp/tests/tests.go
@@ -246,7 +246,7 @@
 	o.CompletionBudget = time.Minute
 	o.HierarchicalDocumentSymbolSupport = true
 	o.SemanticTokens = true
-	o.InternalOptions.NewDiff = "both"
+	o.InternalOptions.NewDiff = "new"
 }
 
 func RunTests(t *testing.T, dataDir string, includeMultiModule bool, f func(*testing.T, *Data)) {