Remove git dependency on is-true function

The function is currently only being used for checking the result of
`git rev-parse --is-inside-work-tree`. Checking for the return code of
the command is enough.

modules/git/functions/git-commit-lost

@@ -1,4 +1,4 @@
-if ! is-true "$(command git rev-parse --is-inside-work-tree 2> /dev/null)"; then
+if ! command git rev-parse --is-inside-work-tree >/dev/null 2>&1; then
   print "${0}: not a repository work tree: ${PWD}" >&2
   return 1
 fi

modules/git/functions/git-stash-clear-interactive

@@ -1,4 +1,4 @@
-if ! is-true "$(command git rev-parse --is-inside-work-tree 2> /dev/null)"; then
+if ! command git rev-parse --is-inside-work-tree >/dev/null 2>&1; then
   print "${0}: not a repository work tree: ${PWD}" >&2
   return 1
 fi

modules/git/functions/git-stash-dropped

@@ -1,4 +1,4 @@
-if ! is-true "$(command git rev-parse --is-inside-work-tree 2> /dev/null)"; then
+if ! command git rev-parse --is-inside-work-tree >/dev/null 2>&1; then
   print "${0}: not a repository work tree: ${PWD}" >&2
   return 1
 fi

modules/git/functions/git-stash-recover

@@ -1,4 +1,4 @@
-if ! is-true "$(command git rev-parse --is-inside-work-tree 2> /dev/null)"; then
+if ! command git rev-parse --is-inside-work-tree >/dev/null 2>&1; then
   print "${0}: not a repository work tree: ${PWD}" >&2
   return 1
 fi

modules/git/functions/git-submodule-move

@@ -1,4 +1,4 @@
-if ! is-true "$(command git rev-parse --is-inside-work-tree 2> /dev/null)"; then
+if ! command git rev-parse --is-inside-work-tree >/dev/null 2>&1; then
   print "${0}: not a repository work tree: ${PWD}" >&2
   return 1
 elif [[ "${PWD}" != "$(git-root)" ]]; then

modules/git/functions/git-submodule-remove

@@ -1,4 +1,4 @@
-if ! is-true "$(command git rev-parse --is-inside-work-tree 2> /dev/null)"; then
+if ! command git rev-parse --is-inside-work-tree >/dev/null 2>&1; then
   print "${0}: not a repository work tree: ${PWD}" >&2
   return 1
 elif [[ "${PWD}" != "$(git-root)" ]]; then