<i18n dev> RFR: 8337279: Optimize format instant

[Shaojin Wen]

By removing the redundant code logic in DateTimeFormatterBuilder$InstantPrinterParser#formatTo, the codeSize can be reduced and the performance can be improved.

-------------

Commit messages:
 - optimize format instant

Changes: https://git.openjdk.org/jdk/pull/20353/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20353&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8337279
  Stats: 43 lines in 2 files changed: 7 ins; 31 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/20353.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20353/head:pull/20353

PR: https://git.openjdk.org/jdk/pull/20353