RFR: 8293324: ciField.hpp has two methods to return field's offset

[Ilya Korennoy]

Small refactoring of ciField.hpp method `offset()` removed and  `offset_in_bytes()` used instead.

Test: tier1 linux-x86_64

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Commit messages:
 - 8293324: Remove method offset from ciField.hpp and use offset_in_bytes instead

Changes: https://git.openjdk.org/jdk/pull/13003/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13003&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8293324
  Stats: 20 lines in 10 files changed: 0 ins; 5 del; 15 mod
  Patch: https://git.openjdk.org/jdk/pull/13003.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/13003/head:pull/13003

PR: https://git.openjdk.org/jdk/pull/13003