Remove second embedding of assert.constraints fragment (#1972)

The fragment for embedding assert.constraint section has been accidently
added twice. This PR is cleaning up this inconsistency

Author: StefanHenke

guides/providing-services.md

@@ -942,8 +942,6 @@ entity Person : cuid {
 
 Next to input validation, you can add [database constraints](databases#database-constraints) to prevent invalid data from being persisted.
 
-<div id="assertconstraints" />
-
 ## Custom Logic