Remove refs to Parallel tests

Author: gonzaloserrano

style.md

@@ -3896,10 +3896,6 @@ While there are no strict guidelines, readability and maintainability should
 always be top-of-mind when deciding between Table Tests versus separate tests
 for multiple inputs/outputs to a system.
 
-#### Parallel Tests
-
-Run `t.Parallel()` to improve the performance of your test cases.
-
 <!-- TODO: Explain how to use _test packages. -->
 
 ### Functional Options