RFR: 8254776: Remove unimplemented LowMemoryDetector::check_memory_usage [v2]

[Aleksey Shipilev]

> `LowMemoryDetector::check_memory_usage` seems declared but not implemented. Current history does not show any
> definitions since the initial load. Can be removed.
> Testing:
>  - [x] Linux x86_64 build
>  - [x] Test search for `check_memory_usage` in `src/hotspot`

Aleksey Shipilev has updated the pull request with a new target base due to a merge or a rebase. The pull request now
contains one commit:

  8254776: Remove unimplemented LowMemoryDetector::check_memory_usage

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Changes: https://git.openjdk.java.net/jdk/pull/659/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=659&range=01
  Stats: 1 line in 1 file changed: 0 ins; 1 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/659.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/659/head:pull/659

PR: https://git.openjdk.java.net/jdk/pull/659