RFR: 8255338: CodeSections are never frozen

[Claes Redestad]

CodeSections are never actually frozen, so code for freezing can be removed along with some assertions and guarantees.

A few other minor cleanups, too.

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Commit messages:
 - CodeSections are never frozen

Changes: https://git.openjdk.java.net/jdk/pull/834/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=834&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8255338
  Stats: 79 lines in 3 files changed: 0 ins; 77 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/834.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/834/head:pull/834

PR: https://git.openjdk.java.net/jdk/pull/834