RFR: 8296162: [aarch64] Remove unused Address::_is_lval

[Kim Barrett]

Please review this trivial change to remove the unused Address::_is_lval member.

-------------

Commit messages:
 - remove unused _is_lval

Changes: https://git.openjdk.org/jdk/pull/10928/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10928&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8296162
  Stats: 7 lines in 2 files changed: 0 ins; 7 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/10928.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10928/head:pull/10928

PR: https://git.openjdk.org/jdk/pull/10928