fix(bigtable): remove heartbeat miss logging (#14054)

We already capture heartbeat closes in close reason. So this is visible
from server side metrics. Logging warning could spam application logs.

Author: mutianf

java-bigtable/google-cloud-bigtable/src/main/java/com/google/cloud/bigtable/data/v2/internal/session/SessionImpl.java

@@ -538,8 +538,6 @@ private void checkHeartbeat() {
       return;
     }
     if (clock.instant().isAfter(nextHeartbeat)) {
-      logger.warning(
-          String.format("Missed heartbeat for %s, forcing session close", info.getLogName()));
       forceClose(MISSED_HEARTBEAT_CLOSE_REQUEST);
       return;
     }