Update the testing doc to remove some stale information (AOT_MODULES, removed
in [JDK-8264805](https://bugs.openjdk.org/browse/JDK-8264805)) and fix some
spelling issues.
Testing: tier1
-------------
Commit messages:
- 8332849: Update doc/testing.{md,html} (spelling and stale information)
Changes: https://git.openjdk.org/jdk/pull/19375/files
Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19375&range=00
Issue: https://bugs.openjdk.org/browse/JDK-8332849
Stats: 46 lines in 2 files changed: 0 ins; 28 del; 18 mod
Patch: https://git.openjdk.org/jdk/pull/19375.diff
Fetch: git fetch https://git.openjdk.org/jdk.git pull/19375/head:pull/19375
PR: https://git.openjdk.org/jdk/pull/19375
