Revert "Generate deprecation warning for postgresql"

Based on resolution [1], there's no clear indication that next
steps involve the removal of the DB from Devstack or from the gate.

[1] I332cef8ec4539520adcf37c6d2ea11488289fcfd

This reverts commit d9aaae95f2b84170bf35e037715e4963d89f940c.

Change-Id: I8410d65c0e0b24035aa035fac7560a686d53ec50
diff --git a/lib/databases/postgresql b/lib/databases/postgresql
index 618834b..1f347f5 100644
--- a/lib/databases/postgresql
+++ b/lib/databases/postgresql
@@ -95,7 +95,6 @@
 
 function install_database_postgresql {
     echo_summary "Installing postgresql"
-    deprecated "Use of postgresql in devstack is deprecated, and will be removed during the Pike cycle"
     local pgpass=$HOME/.pgpass
     if [[ ! -e $pgpass ]]; then
         cat <<EOF > $pgpass