RFR: 7903135: Correct license file

[Dmitry Bessonov]

The JT Harness repository doesn't have a LICENSE file.
It contains `legal/license.txt`.
We need to place a proper LICENSE file to the repository root.

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Commit messages:
 - 7903135: Correct license file

Changes: https://git.openjdk.java.net/jtharness/pull/26/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jtharness&pr=26&range=00
  Issue: https://bugs.openjdk.java.net/browse/CODETOOLS-7903135
  Stats: 30 lines in 2 files changed: 5 ins; 5 del; 20 mod
  Patch: https://git.openjdk.java.net/jtharness/pull/26.diff
  Fetch: git fetch https://git.openjdk.java.net/jtharness pull/26/head:pull/26

PR: https://git.openjdk.java.net/jtharness/pull/26