all: remove reliance on --compact-summary

This flag is recently added to git. Avoid it for now.

Change-Id: I007f3cc12ec6ef37bc6d70ddc346b7af7983879e
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/220501
Reviewed-by: Damien Neil <dneil@google.com>
diff --git a/integration_test.go b/integration_test.go
index a408c82..191d2e7 100644
--- a/integration_test.go
+++ b/integration_test.go
@@ -53,7 +53,7 @@
 	// going through all the presubmits.
 	//
 	// Fail the test late, so we can test uncommitted changes with -failfast.
-	diff := mustRunCommand(t, "git", "diff", "--compact-summary", "HEAD")
+	diff := mustRunCommand(t, "git", "diff", "HEAD")
 	if strings.TrimSpace(diff) != "" {
 		fmt.Printf("WARNING: working tree contains uncommitted changes:\n%v\n", diff)
 	}