RFR: 8309110: Build failure after JDK-8307795 due to warnings in micro-benchmark StoreMaskTrueCount.java

[Jie Fu]

Just remove the `static` to fix the build failure.
Thanks.

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Commit messages:
 - 8309110: Build failure after JDK-8307795 due to warnings in micro-bechmark StoreMaskTrueCount.java

Changes: https://git.openjdk.org/jdk/pull/14218/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14218&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8309110
  Stats: 4 lines in 1 file changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/14218.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14218/head:pull/14218

PR: https://git.openjdk.org/jdk/pull/14218