Abilty to remove key during merge
Add missing file
Remove phpdocs
Changes in removekey class
Move to own namespace
Create separate test
#6899 - importing `MergeRemoveKey` class
#6899 - avoiding unused variable assignment
#6899 - adding `@group` annotation for newly introduced tests
#6899 - optimized imports
Merge branch 'feature/#6899-arrayutils-merge-ability-to-remove-keys' into develop

Close #6899