RFR: 8274835: Remove unnecessary castings in java.base

[Andrey Turbanov]

Redundant castings make code harder to read.
Found them by IntelliJ IDEA.
I tried to select only casts which are definitely safe to remove. Also didn't touch primitive types casts.

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Commit messages:
 - [PATCH] Remove unnecessary castings in java.base
 - [PATCH] Remove unnecessary castings in java.base

Changes: https://git.openjdk.java.net/jdk/pull/5454/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5454&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8274835
  Stats: 38 lines in 15 files changed: 1 ins; 4 del; 33 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5454.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5454/head:pull/5454

PR: https://git.openjdk.java.net/jdk/pull/5454