Fix require for mysql_service

Starting with [0] grains are provided via salt-formula metadata.
This patch removes broken require for mysql_service as 'mysql_salt_config'
is not defined any more.

[0] https://gerrit.mcp.mirantis.net/4297/

Change-Id: Id7acea75161ea79259f00df4081dcda844119f58
diff --git a/mysql/common.sls b/mysql/common.sls
index 5173cca..db221d4 100644
--- a/mysql/common.sls
+++ b/mysql/common.sls
@@ -40,8 +40,6 @@
   - watch:
     - file: mysql_config
   {%- endif %}
-  - require:
-    - file: mysql_salt_config
 {%- endif %}