Tweaks

• LearnDash requirement has been updated to 4.6.0.
• Updated required PHP version to 7.4.
• Updated required WP version to 6.6.
• Added actions: learndash_zapier_uninstall.
• Deprecated classes: LearnDash_Dependency_Check_LD_Zapier.
• Deprecated functions: learndash_zapier_check_dependency.