Abolish EditorConfig kludge in favour of user preferences

GitHub now allows users to choose their preferred tab-width (under their
account's "Appearance" settings). Moreover, using EditorConfig to affect
the sizes of rendered tabs is no longer possible (community/community#5813).

More info: 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
 
 [config.cson]
 trim_trailing_whitespace = true
@@ -16,7 +15,9 @@ end_of_line = crlf
 
 [*.{yml,yaml}]
 indent_style = space
+indent_size = 4
 
 [.git/COMMIT_EDITMSG]
 indent_style = space
+indent_size = 4
 max_line_length = 72