feat(shell): let the delta theme be defined by base16-shell

When using light and dark theme I had to keep changing the git config so
git diff was readable. I have found that base16 shell has built in
support for delta so we can remove this config and let base16 shell deal
with it.

See: 9706041539/hooks/base16-delta.sh

site-modules/core/templates/git/gitconfig.erb

@@ -29,7 +29,6 @@
   diffFilter = delta --color-only
 
 [delta]
-  light = true
   line-numbers = true
   navigate = true
   hunk-header-style = raw