RFR: 8234534: Simplify CardTable code after CMS removal

[Thomas Schatzl]

Hi,

  can I have reviews for this cleanup that removes CMS specific code from `CardTable/CardTableRS`?

Note that there is still this "conc_scan" parameter passed to the card table that affects barrier code generation, for some reason also G1 barrier code generation although it should not as `G1CardTable::scanned_concurrently()` only used for the "normal" card table. Initial attempts showed that removing this is not straightforward, causing crashes and so I left it out for [JDK-8250941](https://bugs.openjdk.java.net/browse/JDK-8260941) so that this change is solely about removing unused code.

Testing: tier1-4, some tier1-5 runs earlier (before some removal of hunks for files only containing copyright updates or newline changes)

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Commit messages:
 - Initial commit

Changes: https://git.openjdk.java.net/jdk/pull/2354/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2354&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8234534
  Stats: 197 lines in 7 files changed: 0 ins; 185 del; 12 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2354.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2354/head:pull/2354

PR: https://git.openjdk.java.net/jdk/pull/2354