RFR: JDK-8305504: stutter typo in java.compiler files

[Jonathan Gibbons]

Please review a trivial doc-only edit to fix an issue in a recent addition of some RFC `@spec` tags

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Commit messages:
 - JDK-8305504: stutter typo in java.compiler files

Changes: https://git.openjdk.org/jdk/pull/13316/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13316&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8305504
  Stats: 4 lines in 2 files changed: 2 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/13316.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13316/head:pull/13316

PR: https://git.openjdk.org/jdk/pull/13316