Use `command` and `type` instead of `which` (#2144)

`which` has been deprecated in Debian's debianutils 5.0+
They suggest using `type` and `command` as replacements:
3a8dd10b45 ,
610a65c6ef

plugins/python-build/test/pyenv.bats

@@ -183,7 +183,7 @@ OUT
 }
 
 @test "pyenv-install has usage help preface" {
-  run head "$(which pyenv-install)"
+  run head "$(command -v pyenv-install)"
   assert_output_contains 'Usage: pyenv install'
 }
 
@@ -212,6 +212,6 @@ OUT
 }
 
 @test "pyenv-uninstall has usage help preface" {
-  run head "$(which pyenv-uninstall)"
+  run head "$(command -v pyenv-uninstall)"
   assert_output_contains 'Usage: pyenv uninstall'
 }

test/test_helper.bash

@@ -116,12 +116,12 @@ path_without() {
   local path=":${PATH}:"
   for exe; do 
     local found alt util
-    for found in $(PATH="$path" which -a "$exe"); do
+    for found in $(PATH="$path" type -aP "$exe"); do
       found="${found%/*}"
       if [ "$found" != "${PYENV_ROOT}/shims" ]; then
         alt="${PYENV_TEST_DIR}/$(echo "${found#/}" | tr '/' '-')"
         mkdir -p "$alt"
-        for util in bash head cut readlink greadlink which; do
+        for util in bash head cut readlink greadlink; do
           if [ -x "${found}/$util" ]; then
             ln -s "${found}/$util" "${alt}/$util"
           fi