Add latest.txt as per new format discussed in #7336

Remove make-latest.sh, since there's now more information than we can sensibly construct from the command line - the file should now be uploaded to releases.wagtail.io with `./latest.sh put latest.txt`.

scripts/latest.txt

@@ -0,0 +1,10 @@
+{
+    "version": "2.13.4",
+    "url":     "https://docs.wagtail.io/en/stable/releases/2.13.4.html",
+    "majorUrl": "https://docs.wagtail.io/en/stable/releases/2.13.html",
+    "lts": {
+        "version": "2.11.8",
+        "url": "https://docs.wagtail.io/en/stable/releases/2.11.8.html",
+        "majorUrl": "https://docs.wagtail.io/en/stable/releases/2.11.html"
+    }
+}

scripts/make-latest.sh

@@ -1,43 +0,0 @@
-#! /bin/sh
-# vim:sw=4 ts=4 et:
-
-version=""
-url="https://wagtail.io"
-
-while [ ! -z "$1" ]; do
-    case "$1" in
-        --version=*)
-            version=$(echo "$1" | sed -e 's/^--version=//')
-            ;;
-        --url=*)
-            url=$(echo "$1" | sed -e 's/^--url=//')
-            ;;
-        *)
-            printf >&2 -- '%s: unknown argument "%s"\n' "$0"
-            printf >&2 -- 'usage: %s --version=<version> [--url=<url>]\n' "$0"
-            exit 1
-    esac
-    shift
-done
-
-if [ -z "$version" ]; then
-    printf >&2 -- '%s: must specify --version\n' "$0"
-    printf >&2 -- 'usage: %s --version=<version> [--url=<url>]\n' "$0"
-    exit 1
-fi
-
-LTMP=$(mktemp "${TMPDIR:-/tmp}/latest.XXXXXX")
-if [ "$?" -ne 0 ]; then
-    printf >&2 -- '%s: cannot create temporary file\n' "$0"
-    exit 1
-fi
-trap 'rm -f "${LTMP}"' 0 TERM INT
-
-cat >"${LTMP}" <<__EOF__
-{
-    "version": "${version}",
-    "url":     "${url}"
-}
-__EOF__
-
-${0%make-latest.sh}latest.sh put "${LTMP}"