RFR: Remove vestigial command line options and removed unused code

[William Kemper]

* Removed ShenandoahUseSimpleCardScanning and ShenandoahPromoteTenuredRegions command line options
* Removed preprocessor directives FAST_REMEMBERED_SET_SCANNING and CROSSING_OFFSETS_NO_LONGER_NEEDED

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Commit messages:
 - Remove vestigial command line options and ifdef'd code sections

Changes: https://git.openjdk.java.net/shenandoah/pull/85/files
 Webrev: https://webrevs.openjdk.java.net/?repo=shenandoah&pr=85&range=00
  Stats: 169 lines in 4 files changed: 0 ins; 165 del; 4 mod
  Patch: https://git.openjdk.java.net/shenandoah/pull/85.diff
  Fetch: git fetch https://git.openjdk.java.net/shenandoah pull/85/head:pull/85

PR: https://git.openjdk.java.net/shenandoah/pull/85