RFR: 8260941: Remove the conc_scan parameter for CardTable

[Thomas Schatzl]

Hi,

  can I have reviews for this removal of the last(?) CMS-specific code in CardTable, namely some provision to indicate that cards are being scanned concurrently in Serial/Parallel GC barrier code?

The change simply follows the predicate into Serial/Parallel GC code which always returns false for them and removes that code.

In the review for JDK-8234534 I mentioned that I split this out due to unexplainable errors; testing tier1-5 three times showed none of that any more (after updating to latest code).

This change has only been built on Oracle-platforms and linux-x86 via github actions (https://github.com/tschatzl/jdk/actions/runs/539993964), so I would like to kindly ask maintainers of the others to compile and report issues (32 bit ARM, PPC etc).

Testing: tier1-5

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Commit messages:
 - Remove scan_concurrently()
 - Compilation fixes
 - First attempt to prune code

Changes: https://git.openjdk.java.net/jdk/pull/2425/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2425&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8260941
  Stats: 81 lines in 17 files changed: 4 ins; 66 del; 11 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2425.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2425/head:pull/2425

PR: https://git.openjdk.java.net/jdk/pull/2425