RFR: 8304880: [PPC64] VerifyOops code in C1 doesn't work with ZGC

[Martin Doerr]

I suggest to remove this code for the following reasons:
- It doesn't work with ZGC (oop needs to go through load barrier, see JBS issue).
- It generates too much code. Loading oops is quite common and the oop verification code is quite lengthy.
- Other platforms don't have it, either.

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Commit messages:
 - 8304880: [PPC64] VerifyOops code in C1 doesn't work with ZGC

Changes: https://git.openjdk.org/jdk/pull/13175/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13175&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8304880
  Stats: 8 lines in 1 file changed: 0 ins; 8 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/13175.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13175/head:pull/13175

PR: https://git.openjdk.org/jdk/pull/13175