Remove reference to CriticalPathComputer so that garbage can be cleaned up after a build.

RELNOTES: None.

Closes #9160.

PiperOrigin-RevId: 263146101

src/main/java/com/google/devtools/build/lib/runtime/BuildSummaryStatsModule.java

diff --git a/src/main/java/com/google/devtools/build/lib/runtime/BuildSummaryStatsModule.java b/src/main/java/com/google/devtools/build/lib/runtime/BuildSummaryStatsModule.java
index f2c55b7..ead6763 100644
--- a/src/main/java/com/google/devtools/build/lib/runtime/BuildSummaryStatsModule.java
+++ b/src/main/java/com/google/devtools/build/lib/runtime/BuildSummaryStatsModule.java
@@ -189,7 +189,10 @@
       event.getResult().getBuildToolLogCollection()
           .addDirectValue("process stats", spawnSummary.getBytes(StandardCharsets.UTF_8));
     } finally {
-      criticalPathComputer = null;
+      if (criticalPathComputer != null) {
+        eventBus.unregister(criticalPathComputer);
+        criticalPathComputer = null;
+      }
       profilePath = null;
     }
   }