chore: Remove CTA A/B Testing legacy system

This feature was not part of the current development phase.

Deleted files:
- Inc/cta-ab-testing.php (A/B testing implementation)
- Inc/customizer-cta.php (WordPress Customizer settings + Google Analytics)
- TemplateParts/content-cta.php (CTA template part)
- Assets/Js/cta-tracking.js (GA4 tracking script)

Modified files:
- functions.php: Remove require_once for deleted files
- functions-addon.php: Remove CTA loading references
- Inc/enqueue-scripts.php: Remove roi_enqueue_cta_assets() function

Note: CTA components in Admin Panel (CtaBoxSidebar, CtaLetsTalk, CtaPost)
are NOT affected - they are part of the Clean Architecture system.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

TemplateParts/content-cta.php

@@ -1,29 +0,0 @@
-<?php
-/**
- * Template part for displaying CTA with A/B testing
- *
- * Este template renderiza el Call-to-Action con A/B Testing.
- * La variante (A o B) se determina automáticamente por usuario.
- *
- * @package ROI_Theme
- * @since 1.0.0
- */
-
-// Exit if accessed directly
-if (!defined('ABSPATH')) {
-    exit;
-}
-
-// Solo mostrar en posts individuales
-if (!is_single()) {
-    return;
-}
-
-// Verificar si el CTA está habilitado
-$enable_cta = get_theme_mod('roi_enable_cta', true);
-if (!$enable_cta) {
-    return;
-}
-
-// Usar la función del sistema de A/B testing
-roi_display_cta();