RFR: 8322927: Unused code in LIR_Assembler::verify_oop_map

[Koichi Sakata]

This is a trivial change to remove unused code.

Methods like as_string() or freeze() are not called for the stringStream object, so these are unused code. The object was used before the SPARC port was removed (071bd521bca).

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Commit messages:
 - Update the copyright
 - Remove unused code

Changes: https://git.openjdk.org/jdk/pull/17721/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17721&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8322927
  Stats: 3 lines in 1 file changed: 0 ins; 2 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/17721.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17721/head:pull/17721

PR: https://git.openjdk.org/jdk/pull/17721