Revert "Make lots of tests run in parallel"

This reverts commit 323dc60712.

Reason for revert: Possible cause of test instability
Bug: 170513220
Test: soong tests

Change-Id: Iee168e9fbb4210569e6cffcc23e60d111403abb8

android/defaults_test.go

@@ -59,7 +59,6 @@ func defaultsTestDefaultsFactory() Module {
 }
 
 func TestDefaults(t *testing.T) {
-	t.Parallel()
 	bp := `
 		defaults {
 			name: "transitive",
@@ -103,7 +102,6 @@ func TestDefaults(t *testing.T) {
 }
 
 func TestDefaultsAllowMissingDependencies(t *testing.T) {
-	t.Parallel()
 	bp := `
 		defaults {
 			name: "defaults",