RFR: 8300863: Remove C-style array declarations in java.io

[Per Minborg]

Some variables are declared using old-style declarations. These should be modified to conform to modern style. 

This is a task derived from https://github.com/openjdk/jdk/pull/11848

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Commit messages:
 - Fix more classes
 - Remove c-style declarations

Changes: https://git.openjdk.org/jdk/pull/12139/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12139&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8300863
  Stats: 21 lines in 8 files changed: 1 ins; 1 del; 19 mod
  Patch: https://git.openjdk.org/jdk/pull/12139.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12139/head:pull/12139

PR: https://git.openjdk.org/jdk/pull/12139