RFR: Fix jtreg build with /usr/bin/git available

[Jan Kratochvil]

I have tried to rebase JTREG on top of `jt6.0-b23` or `master` of jtharness but with `/usr/bin/git` available JTREG then does not build:

generate.release.file:
BUILD FAILED
.../jtreg/build/deps/jtharness/src/jtharness-jt6.0-b23/build/build.xml:277: exec returned: 128

This reverts a part of commit [8a0bc39980118fc47d9fbe161f1bc1fa75aa854b](https://github.com/openjdk/jtharness/commit/8a0bc39980118fc47d9fbe161f1bc1fa75aa854b) by @dbessono where this change is not described and it may have been unintentional.
Unforunately I am not yet Author so I do not yet have a JBS account so I cannot file it to JBS (Java Bug System).

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Commit messages:
 - Fix jtreg build with /usr/bin/git available

Changes: https://git.openjdk.org/jtharness/pull/34/files
 Webrev: https://webrevs.openjdk.org/?repo=jtharness&pr=34&range=00
  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jtharness/pull/34.diff
  Fetch: git fetch https://git.openjdk.org/jtharness pull/34/head:pull/34

PR: https://git.openjdk.org/jtharness/pull/34