prezto/modules/git/functions/git-submodule-remove

#
# Removes a Git submodule.
#
# Authors:
#   Sorin Ionescu <sorin.ionescu@gmail.com>
#

if ! is-true "$(command git rev-parse --is-inside-work-tree 2> /dev/null)"; then
  print "$0: not a repository work tree: $PWD" >&2
  return 1
elif [[ "$PWD" != "$(git-root)" ]]; then
  print "$0: must be run from the root of the work tree" >&2
  return 1
elif ! command git config --file .gitmodules --get "submodule.${1}.path" &>/dev/null; then
  print "$0: submodule not found: $1" >&2
  return 1
fi

command git config --file "$(git-dir)/config" --remove-section "submodule.${1}" &>/dev/null
command git config --file "$(git-root)/.gitmodules" --remove-section "submodule.${1}" &>/dev/null
command git add .gitmodules

command git rm --cached -rf "${1}"
rm -rf "${1}"
rm -rf "$(git-dir)/modules/${1}"

return 0