To remove the secondary menu items from the mobile menu go to Divi -> Theme Customizer -> Mobile Menu Customizer -> Menu Settings and find the SECONDARY MENU ITEMS POSITION setting and select the Remove secondary menu items option.
To remove the secondary menu items from the mobile menu go to Divi -> Theme Customizer -> Mobile Menu Customizer -> Menu Settings and find the SECONDARY MENU ITEMS POSITION setting and select the Remove secondary menu items option.