unset all aliases before setting any user alias

This was notorious to detect but `command -v ls` would return
"alias ls='ls --color=tty'" because (on NixOS), '/etc/bashrc' has an
alias set for 'ls'. I already have custom aliases that are "more fancy",
so unset all such aliases.

.bashrc

@@ -2,6 +2,7 @@
 # The above directive disables https://www.shellcheck.net/wiki/SC2139
 dash "${HOME}/.local/scripts/other-common-scripts/alacritty-import.sh"
 
+unalias -a
 if [[ "$(uname)" == 'Linux' ]]; then
     GNU_LS="$(command -v ls)"
     GNU_GREP="$(command -v grep)"