doc/luaxform: Remove init function from example

Issue: 8035

The `luaxform` transform doesn't support the `init` function. This
commit removes that from the example and clarifies how functions in the
Lua script are used.

(cherry picked from commit b02d9bb4f1)

doc/userguide/rules/transforms.rst

@@ -295,6 +295,8 @@ to a buffer.
 Lua scripts that are used for transformations *must* contain a function
 named ``transform``.
 
+Lua scripts can have other functions; Suricata only invokes the ``transform`` function.
+
 Lua transforms can be passed optional arguments -- see the examples below -- but they
 are not required to do so. Arguments are comma-separated.
 
@@ -341,11 +343,6 @@ the buffer.
 
 .. code-block:: lua
 
-   function init (args)
-        local needs = {}
-        return needs
-   end
-
    local function get_value(item, key)
        if string.find(item, key) then
            local _, value = string.match(item, "(%a+)%s*(%d*)")