vim:ftplugin: Adjust to new colorcolumn settings

Since
a98457e66b ("vim:autocmd: Adjust colorcolumn with &textwidth")
or correctly sine
fc0969abba ("vim: Drop textwidth autocmd for native way")
it is not necessary to add the `textwidth` manually to `colorcolumn`.
The colorcolumns are now also placed *behind* textwidth.

.config/vim/ftplugin/gitcommit.vim

@@ -1,5 +1,5 @@
 " Shorter lines. Subject should be max 50 and body max 72
-setlocal colorcolumn=50,72
+setlocal colorcolumn+=51
 setlocal textwidth=72
 " Spell checking always enabled
 setlocal spell spelllang=en