RFR: Fix build error on MacOS / Clang 14.0.0

[Aleksey Shipilev]

MacOS / Clang 14.0.0 currently fails with lot of errors like:


/Users/shipilev/Work/shipilev-shenandoah/src/hotspot/share/gc/shenandoah/mode/shenandoahGenerationalMode.hpp:55:16: warning: 'is_generational' overrides a member function but is not marked 'override' [-Winconsistent-missing-override]
  virtual bool is_generational() { return true; }
               ^
/Users/shipilev/Work/shipilev-shenandoah/src/hotspot/share/gc/shenandoah/mode/shenandoahMode.hpp:59:16: note: overridden virtual function is here
  virtual bool is_generational() { return false; }
               ^


Remarkably, no other heuristics are affected by this, even though they do not have `override`-s on them. I think the actual cause is that we use `override` once in the `ShenandoahGenerationalMode`, that is enough to flag this class for inconsistencies. So the easiest fix is to drop `override`.

Additional testing:
 - [x] macos-aarch64-server-fastdebug build

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

Commit messages:
 - Fix

Changes: https://git.openjdk.org/shenandoah/pull/243/files
 Webrev: https://webrevs.openjdk.org/?repo=shenandoah&pr=243&range=00
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/shenandoah/pull/243.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah.git pull/243/head:pull/243

PR: https://git.openjdk.org/shenandoah/pull/243