RFR: 8258408: SystemDictionary passes TRAPS to functions that don't throw exceptions

[Coleen Phillimore]

Please review some mostly superficial cleanups to the SystemDictionary code.  See issue for more details.

Tested with tier1-6.

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Commit messages:
 - Remove some unused includes.
 - 8258408: SystemDictionary passes TRAPS to functions that don't throw exceptions

Changes: https://git.openjdk.java.net/jdk/pull/1808/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1808&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8258408
  Stats: 208 lines in 8 files changed: 38 ins; 71 del; 99 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1808.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1808/head:pull/1808

PR: https://git.openjdk.java.net/jdk/pull/1808