RFR: 8263041: Shenandoah: Cleanup C1 keep alive barrier check [v2]

[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:

  Aleksey's comment

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/2834/files
  - new: https://git.openjdk.java.net/jdk/pull/2834/files/e324e007..41c6c8d7

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=2834&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=2834&range=00-01

  Stats: 4 lines in 3 files changed: 0 ins; 1 del; 3 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