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

cmd/extract_apks/main_test.go

@@ -37,7 +37,6 @@ type testDesc struct {
 }
 
 func TestSelectApks_ApkSet(t *testing.T) {
-	t.Parallel()
 	testCases := []testDesc{
 		{
 			protoText: `
@@ -267,7 +266,6 @@ variant {
 }
 
 func TestSelectApks_ApexSet(t *testing.T) {
-	t.Parallel()
 	testCases := []testDesc{
 		{
 			protoText: `
@@ -444,7 +442,6 @@ type testCaseWriteApks struct {
 }
 
 func TestWriteApks(t *testing.T) {
-	t.Parallel()
 	testCases := []testCaseWriteApks{
 		{
 			name:       "splits",