RFR: 8281637: Remove unused VerifyOption_G1UseNextMarking [v2]

[Stefan Johansson]

> Please review this change to remove an unused verification option.
> 
> **Summary**
> In G1 there have been three different `VerifyOption` that can be passed to verification to signal how to determine liveness. One of these options, `VerifyOption_G1UseNextMarking`,  has been unused for quite some time and this change removes it. When removing it the `G1CollectedHeap::is_obj_ill(...)` functions are more or less unused, so I removed those as well and inlined the checks in the only place where it is really used `G1CMIsAliveClosure::do_object_b(...)`
> 
> **Testing**
> 
> - [x] Mach5
> - [x] Local verification testing

Stefan Johansson has updated the pull request incrementally with two additional commits since the last revision:

 - Update src/hotspot/share/gc/g1/g1ConcurrentMark.inline.hpp
   
   Co-authored-by: Thomas Schatzl <59967451+tschatzl at users.noreply.github.com>
 - Update src/hotspot/share/gc/g1/g1ConcurrentMark.inline.hpp
   
   Co-authored-by: Thomas Schatzl <59967451+tschatzl at users.noreply.github.com>

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/7440/files
  - new: https://git.openjdk.java.net/jdk/pull/7440/files/11e02017..d1439e42

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=7440&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=7440&range=00-01

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7440.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7440/head:pull/7440

PR: https://git.openjdk.java.net/jdk/pull/7440