RFR: 8324765: C2 SuperWord: remove dead code: SuperWord::insert_extracts

[Emanuel Peter]

Subtask of https://github.com/openjdk/jdk/pull/16620

As far as all tests and code study have showed me, SuperWord::insert_extracts is dead.

I am replacing it with verification code, that checks that no ExtractNode is required.

**Details**

All the relevant cases are marked as "unprofitable" in `SuperWord::profitable`, see:
https://github.com/openjdk/jdk/blob/dfdd2174d7af5e3e995147484db17b45b006f6d0/src/hotspot/share/opto/superword.cpp#L1912-L1915

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Commit messages:
 - fix reduction case
 - 8324765

Changes: https://git.openjdk.org/jdk/pull/17589/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17589&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8324765
  Stats: 54 lines in 2 files changed: 3 ins; 28 del; 23 mod
  Patch: https://git.openjdk.org/jdk/pull/17589.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17589/head:pull/17589

PR: https://git.openjdk.org/jdk/pull/17589