DOC: No need for titles in templates

.gitlab/issue_templates/bugs.md

-## Title of the bug
-
 ### Description
 
 Describe what happens and why you think it is a bug

.gitlab/issue_templates/documentation_changes.md

-## Title of the documentation change requested
-
 ### Target documentation ressources
 
 Can be a combination of Software guide, cookbook, doxygen, blog, applications doc, websites

.gitlab/issue_templates/feature_request.md

-## Title of the requested feature
-
 Short summary of the requested feature

.gitlab/issue_templates/request_for_comments.md

-## Title of the resquest for comments
-
 ### What changes will be made and why they would make a better Orfeo ToolBox?
 
 #### High level description

.gitlab/merge_request_templates/request_for_changes.md

-## Title of the Request for Changes
-
 ### Summary
 
 Gives a short summary of the changes.