Remove pyenv and add new shell theme

I enjoyed bobthefish quite a bit, but the nerd fonts on the CLI were
screwing up Emacs, and that's a non-starter for me.

One thing I like about cmorrell is that it has the host in the terminal
line, so I can tell which machine I'm on.

config/fish/functions/fish_greeting.fish

@@ -1,6 +0,0 @@
-function fish_greeting -d "What's up, fish?"
-  set_color $fish_color_autosuggestion
-  uname -nmsr
-  uptime
-  set_color normal
-end