RFR: 8292285: C2: remove unreachable block after NeverBranch-to-Goto conversion

[Roberto Castañeda Lozano]

`NeverBranch` nodes introduce fake branches out of infinite loops to simplify intermediate optimizations that assume full reachability:
![before](https://user-images.githubusercontent.com/8792647/184355521-8b54725e-f7d2-4d37-a7ba-e0f7d1086421.png)
`PhaseCFG::convert_NeverBranch_to_Goto()` transforms such nodes into simple `Goto` nodes, removing the fake branch and thus making its destination block unreachable:
![after](https://user-images.githubusercontent.com/8792647/184355553-3b862832-7302-4de2-aa29-86d7da0d985a.png)
This changeset removes the unreachable destination block created by `PhaseCFG::convert_NeverBranch_to_Goto()` from the list of basic blocks:
![after-removal](https://user-images.githubusercontent.com/8792647/184355581-82038683-3f4f-4f4f-a8d7-16e507bfdf0c.png)
Removing unreachable blocks created by `PhaseCFG::convert_NeverBranch_to_Goto()` simplifies late control-flow analysis (for example, recomputing dominators during the output phase as required for late barrier analysis in Generational ZGC) and slightly reduces the size of the generated code.

#### Testing

- hs-tier1-3 (windows-x64, linux-x64, linux-aarch64, and macosx-x64; release and debug mode). The changeset does not introduce new test cases because it is already exercised by at least two existing ones (`compiler/inlining/StringConcatInfiniteLoop.java`, `compiler/loopopts/TestInfiniteLoopNotInnerMost.java`).
- fuzzing (~30 min. on each platform).

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Commit messages:
 - Simplify comment
 - Remove unreachable blocks after 'convert_NeverBranch_to_Goto'

Changes: https://git.openjdk.org/jdk/pull/9853/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9853&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8292285
  Stats: 13 lines in 1 file changed: 13 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/9853.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9853/head:pull/9853

PR: https://git.openjdk.org/jdk/pull/9853