[crac] RFR: 8374614: [CRaC] Remove defunct marking

[Radim Vansa]

When initializing fdinfos, there might be a racy native thread closing FD between enumerating FDs and `readlink /proc/self/fd/XXX`, causing an error and assertion to fail.

Further looking into the code it seems that the fdinfo::mark is not read since https://github.com/openjdk/crac/commit/4b0dc2dc9722945579c9772b335a44fa79f1729f and therefore the whole check is defunct, and can be removed.

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Commit messages:
 - 8374614: [CRaC] Remove defunct marking

Changes: https://git.openjdk.org/crac/pull/284/files
  Webrev: https://webrevs.openjdk.org/?repo=crac&pr=284&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8374614
  Stats: 43 lines in 1 file changed: 0 ins; 43 del; 0 mod
  Patch: https://git.openjdk.org/crac/pull/284.diff
  Fetch: git fetch https://git.openjdk.org/crac.git pull/284/head:pull/284

PR: https://git.openjdk.org/crac/pull/284