util: Remove size from linear_parent creation

None of the callsites took advantage of this, so remove
the feature.  This will help to a next change that will
add an opaque type to represent a linear parent.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/25280>

src/compiler/glsl/opt_dead_code_local.cpp

@@ -310,7 +310,7 @@ dead_code_local_basic_block(ir_instruction *first,
    bool progress = false;
 
    void *ctx = ralloc_context(NULL);
-   void *lin_ctx = linear_alloc_parent(ctx, 0);
+   void *lin_ctx = linear_alloc_parent(ctx);
 
    /* Safe looping, since process_assignment */
    for (ir = first, ir_next = (ir_instruction *)first->next;;