Email folder not being removed after uninstallation of Module

[feho1]

Hi everyone.
I am currently developing a simple module that has emails everything was working fine but then i realized after I reset the module whatever changes I do in
'root/modules/my_module/mail/en/en.html'  and 
'root/modules/my_module/mail/en/en.txt'
was not applying to back office translation email translation system. 
Then I realized even tho I uninstall the module with option checked remove the files from system the module folder was removed but not the folder in 'root/themes/my_custom_theme/modules/my_module/mails/en/en.html and en.txt' was still there. 
The question is how do I remove the folder after uninstalling the module? 
I followed official module development documentation of prestashop.
PS Version: 1.7.6.7
PHP 7.2
Thanks in Advance