RFR: 8368775: Remove outdated comment in OutlineTextRenderer

[Daniel Gredler]

Until [JDK-4138921](https://bugs.openjdk.org/browse/JDK-4138921), `TextLayout` did not accept empty strings in the constructor. This limitation has been removed. However, there is a guard condition in `OutlineTextRenderer` which checks for an empty string before trying to use `TextLayout` which explicitly calls out this limitation in a code comment. We should remove the out-of-date comment but leave the check in as an optimization (see discussion in PR #26947).

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Commit messages:
 - IAE guard is now just an optimization

Changes: https://git.openjdk.org/jdk/pull/27523/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27523&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8368775
  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/27523.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27523/head:pull/27523

PR: https://git.openjdk.org/jdk/pull/27523