Fixes upgrade issues with MySql, along with a few other things:

* All usages of getdate() are changed to the system value
* All usages of newid() are chagned to the system value
* Removes the hacks associated with the above
* Fixes the fluent migrations for table creation for mysql to not double create a PK
* Removes other system field values that actually don't do anthing and shouldn't be used

src/Umbraco.Core/Persistence/SqlSyntax/SqlCeSyntaxProvider.cs

@@ -197,13 +197,13 @@ ORDER BY TABLE_NAME, INDEX_NAME");
             switch (systemMethod)
             {
                 case SystemMethods.NewGuid:
-                    return "NEWID()";
-                case SystemMethods.NewSequentialId:
-                    return "NEWSEQUENTIALID()";
+                    return "NEWID()";                
                 case SystemMethods.CurrentDateTime:
                     return "GETDATE()";
-                case SystemMethods.CurrentUTCDateTime:
-                    return "GETUTCDATE()";
+                //case SystemMethods.NewSequentialId:
+                //    return "NEWSEQUENTIALID()";
+                //case SystemMethods.CurrentUTCDateTime:
+                //    return "GETUTCDATE()";
             }
 
             return null;