RFR: 8348180: Remove mention of include of precompiled.hpp from the HotSpot Style Guide

[Stefan Karlsson]

[JDK-8347909](https://bugs.openjdk.org/browse/JDK-8347909) removed the need for HotSpot devs to include the precompiled.hpp. This is the PR to reflect that.

I know that there is some process around updating the style guide, but I can't find it, so I'm starting with a plain PR.

-------------

Commit messages:
 - 8348180: Remove mention of include of precompiled.hpp from the HotSpot Style Guide

Changes: https://git.openjdk.org/jdk/pull/23210/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23210&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8348180
  Stats: 4 lines in 2 files changed: 0 ins; 4 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/23210.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23210/head:pull/23210

PR: https://git.openjdk.org/jdk/pull/23210