libevent2019: libevent_pthreads.la is never built. don't include it

This commit was SVN r26570.

ompi/mca/mpool/rdma/mpool_rdma_module.c

@@ -414,6 +414,7 @@ int mca_mpool_rdma_deregister(struct mca_mpool_base_module_t *mpool,
     OPAL_THREAD_LOCK(&mpool->rcache->lock);
     reg->ref_count--;
     if(reg->ref_count > 0) {
+        fprintf (stderr, "reference count: %d\n", reg->ref_count);
         OPAL_THREAD_UNLOCK(&mpool->rcache->lock);
         return OMPI_SUCCESS;
     }

opal/mca/event/libevent2019/Makefile.am

@@ -85,7 +85,4 @@ noinst_LTLIBRARIES = $(component_noinst)
 libmca_event_libevent2019_la_SOURCES =$(sources)
 libmca_event_libevent2019_la_LDFLAGS = -module -avoid-version
 libmca_event_libevent2019_la_LIBADD = $(builddir)/libevent/libevent.la
-if OPAL_EVENT_HAVE_THREAD_SUPPORT
-libmca_event_libevent2019_la_LIBADD += $(builddir)/libevent/libevent_pthreads.la
-endif