RFR: 8261309: Remove remaining StoreLoad barrier with UseCondCardMark for Serial/Parallel GC

[Thomas Schatzl]

Hi all,

  can I have reviews for this (tiny) change that removes the last (unconditional) StoreLoad memory barrier for Serial/Parallel GC that has apparently been forgotten to be made conditional on `CardTable::scanned_concurrently()` just removed in [JDK-8260941](https://bugs.openjdk.java.net/browse/JDK-8260941) ?

Thanks,
  Thomas

Testing: automatic compilation via github actions, but this is a quite straightforward removal of a single line...

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Commit messages:
 - Initial commit

Changes: https://git.openjdk.java.net/jdk/pull/2541/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2541&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8261309
  Stats: 1 line in 1 file changed: 0 ins; 1 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2541.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2541/head:pull/2541

PR: https://git.openjdk.java.net/jdk/pull/2541