refactor(install): Remove local from install.sh (#2745)

Have removed the `local`s from `install.sh` to allow the script to work
on ksh.

install/install.sh

@@ -1,7 +1,5 @@
 #!/usr/bin/env sh
 
-# shellcheck disable=SC2039
-
 set -eu
 printf '\n'
 
@@ -44,7 +42,6 @@ has() {
 
 # Gets path to a temporary file, even if
 get_tmpfile() {
-  local suffix
   suffix="$1"
   if has mktemp; then
     printf "%s.%s" "$(mktemp)" "${suffix}"
@@ -57,7 +54,6 @@ get_tmpfile() {
 # Test if a location is writeable by trying to write to it. Windows does not let
 # you test writeability other than by writing: https://stackoverflow.com/q/1999988
 test_writeable() {
-  local path
   path="${1:-}/test.txt"
   if touch "${path}" 2>/dev/null; then
     rm "${path}"
@@ -94,9 +90,9 @@ download() {
 }
 
 unpack() {
-  local archive=$1
-  local bin_dir=$2
-  local sudo=${3-}
+  archive=$1
+  bin_dir=$2
+  sudo=${3-}
 
   case "$archive" in
     *.tar.gz)
@@ -166,10 +162,7 @@ elevate_priv() {
 }
 
 install() {
-  local msg
-  local sudo
-  local archive
-  local ext="$1"
+  ext="$1"
 
   if test_writeable "${BIN_DIR}"; then
     sudo=""
@@ -198,7 +191,6 @@ install() {
 #   - linux_musl (Alpine)
 #   - freebsd
 detect_platform() {
-  local platform
   platform="$(uname -s | tr '[:upper:]' '[:lower:]')"
 
   case "${platform}" in
@@ -221,7 +213,6 @@ detect_platform() {
 #   - arm
 #   - arm64
 detect_arch() {
-  local arch
   arch="$(uname -m | tr '[:upper:]' '[:lower:]')"
 
   case "${arch}" in
@@ -241,9 +232,9 @@ detect_arch() {
 }
 
 detect_target() {
-  local arch="$1"
-  local platform="$2"
-  local target="$arch-$platform"
+  arch="$1"
+  platform="$2"
+  target="$arch-$platform"
 
   if [ "${target}" = "arm-unknown-linux-musl" ]; then
     target="${target}eabihf"
@@ -272,7 +263,7 @@ confirm() {
 }
 
 check_bin_dir() {
-  local bin_dir="$1"
+  bin_dir="$1"
 
   if [ ! -d "$BIN_DIR" ]; then
     error "Installation location $BIN_DIR does not appear to be a directory"
@@ -282,7 +273,6 @@ check_bin_dir() {
   fi
 
   # https://stackoverflow.com/a/11655875
-  local good
   good=$(
     IFS=:
     for path in $PATH; do
@@ -299,11 +289,9 @@ check_bin_dir() {
 }
 
 is_build_available() {
-  local arch="$1"
-  local platform="$2"
-  local target="$3"
-
-  local good
+  arch="$1"
+  platform="$2"
+  target="$3"
 
   good=$(
     IFS=" "