Abolish hardcoded tab-size setting

This became redundant with the introduction of user-configurable tabstop
sizes on GitHub earlier this year. Moreover, the site stopped consulting
EditorConfig files for resolving tab-widths, so the kludge of hardcoding
a preferred `indent_size` setting for one's project is now unnecessary.

References: community/community#4893

Author: Alhadis

.editorconfig

@@ -6,7 +6,6 @@ end_of_line = lf
 insert_final_newline = true
 trim_trailing_whitespace = false
 indent_style = tab
-indent_size = 4
 
 [*.el]
 indent_style = space