RFR: 8263041: Shenandoah: Cleanup C1 keep alive barrier check [v3]

[Zhengyu Gu]

> Please review this cleanup. It appears that JDK-8233339 missed C1 change.
> 
> Test:
> - [x] hotspot_gc_shenandoah

Zhengyu Gu has updated the pull request incrementally with one additional commit since the last revision:

  Removed unrelated change

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/2834/files
  - new: https://git.openjdk.java.net/jdk/pull/2834/files/41c6c8d7..63589415

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=2834&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=2834&range=01-02

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2834.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2834/head:pull/2834

PR: https://git.openjdk.java.net/jdk/pull/2834