RFR: 8286474: Drop --enable-preview from Sealed Classes related tests [v2]

[Aleksey Shipilev]

> There are plenty of tests failing on many architectures due to `--enable-preview` VM code introduced by Loom. This improvement eliminates some of the redundant `--enable-preview` clauses from the Sealed Classes tests, since Sealed Classes have been graduated from preview in JDK 17.
> 
> Additional testing:
>  - [x] Linux x86_64 fastdebug, affected tests still pass
>  - [x] Linux x86_32 fastdebug, affected tests start to pass

Aleksey Shipilev has updated the pull request incrementally with one additional commit since the last revision:

  Review comments

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/8627/files
  - new: https://git.openjdk.java.net/jdk/pull/8627/files/9b1a55a3..1b74acf4

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=8627&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=8627&range=00-01

  Stats: 3 lines in 2 files changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8627.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8627/head:pull/8627

PR: https://git.openjdk.java.net/jdk/pull/8627