vim: don't reset all autocommands on sourcing vimrc

vim: don't reset all autocommands on sourcing vimrc

I'm pretty sure this was added to make sure to not set autocommands that
weren't reset in groups every time. By now, I hope that all autocommands
are reset within their own groups, or at least will be when I'm through
reviewing the vimrc to use with nvim.

Furthermore, this particular reset was unsetting the autocommands set by
nvim's init.lua and specifically lazy.nvim's plugin loading
autocommands. It lead to much confusion when trying to have both
init.lua and vimrc.