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

rust/bindgen_test.go

@@ -20,7 +20,6 @@ import (
 )
 
 func TestRustBindgen(t *testing.T) {
-	t.Parallel()
 	ctx := testRust(t, `
 		rust_bindgen {
 			name: "libbindgen",
@@ -67,7 +66,6 @@ func TestRustBindgen(t *testing.T) {
 }
 
 func TestRustBindgenCustomBindgen(t *testing.T) {
-	t.Parallel()
 	ctx := testRust(t, `
 		rust_bindgen {
 			name: "libbindgen",