Leave default_mpm mode for some services

This commit partially reverts I027ffc35c5a09081a8bd565067cdea234e054666
and set back default_mpm to default value to avoid issues with
Apache update during upgrade/update procedures as changing
mpm mode requires exaclty service restart instead of reload, which
leads to failed service run.

Change-Id: I427de68e2cf4609d2af39a4ae97dcb05b02345bd
Related-Prod: PROD-33599
(cherry-picked from commit 02347c70269d26440332986604d1912c562f05ba)
diff --git a/apache/server/site/aodh.yml b/apache/server/site/aodh.yml
index abeb151..9646e4c 100644
--- a/apache/server/site/aodh.yml
+++ b/apache/server/site/aodh.yml
@@ -10,7 +10,6 @@
   apache:
     server:
       enabled: true
-      default_mpm: event
       modules:
         - wsgi
       site:
diff --git a/apache/server/site/barbican.yml b/apache/server/site/barbican.yml
index efa1ffd..34ad44d 100644
--- a/apache/server/site/barbican.yml
+++ b/apache/server/site/barbican.yml
@@ -8,7 +8,6 @@
   apache:
     server:
       enabled: true
-      default_mpm: event
       modules:
         - wsgi
       site:
diff --git a/apache/server/site/gnocchi.yml b/apache/server/site/gnocchi.yml
index 785f6f2..3be97e1 100644
--- a/apache/server/site/gnocchi.yml
+++ b/apache/server/site/gnocchi.yml
@@ -10,7 +10,6 @@
   apache:
     server:
       enabled: true
-      default_mpm: event
       modules:
         - wsgi
       site:
diff --git a/apache/server/site/panko.yml b/apache/server/site/panko.yml
index fe15a68..ef35c67 100644
--- a/apache/server/site/panko.yml
+++ b/apache/server/site/panko.yml
@@ -10,7 +10,6 @@
   apache:
     server:
       enabled: true
-      default_mpm: event
       modules:
         - wsgi
       site: