Fix splitjoin mappings [vim]
Fix splitjoin mappings [vim]

The let lines didn't work because they happened after the plugin had
already run its course, so unmap instead.

I additionally settled on actual mappings for the plugin commands, so
add those.

benknoble/Dotfiles,benknoble/Dotfiles,benknoble/Dotfiles,benknoble/Dotfiles,benknoble/Dotfiles