User: use update function for password updates (#86419)

* Update password through Update function instead

* Remove duplicated to lower

* Refactor password code

pkg/api/org_invite.go

@@ -270,10 +270,6 @@ func (hs *HTTPServer) CompleteInvite(c *contextmodel.ReqContext) response.Respon
 		}
 	}
 
-	if err := completeInvite.Password.Validate(hs.Cfg); err != nil {
-		return response.Err(err)
-	}
-
 	cmd := user.CreateUserCommand{
 		Email:        completeInvite.Email,
 		Name:         completeInvite.Name,