Don't pass `--no-init` to less when `BAT_PAGER` is explicitly set

[masaeedu]

Hello. I'm running into some issues where git log --graph is no longer clearing the screen after I exit. I believe this is because delta is passing the --no-init argument (along with a few others) to less explicitly. See the screenshot below:

I already have my own set of less configuration options in LESS='-R -F --mouse --wheel-lines=10', and it would be ideal if the tool could avoid overriding the user's explicit settings.

I noticed that a similar problem was recently addressed in bat: sharkdp/bat#749, where their solution was to stop passing --no-init to recent enough versions of less; is it possible that delta is just not depending on a recent enough version of bat?

[da-x]

Pushed a PR for this.