RFR: 8332849: Update doc/testing.{md,html} (spelling and stale information) [v2]

[Mikael Vidstedt]

> 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

Mikael Vidstedt has updated the pull request incrementally with one additional commit since the last revision:

  Revert change to deliberately misspelled variables

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/19375/files
  - new: https://git.openjdk.org/jdk/pull/19375/files/859e52d1..88e930e1

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=19375&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=19375&range=00-01

  Stats: 3 lines in 2 files changed: 0 ins; 0 del; 3 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