Removes the Last Name field from the checkout
<?php
/*
 * Plugin Name: Easy Digital Downloads - Remove Last Name at Checkout
 * Description: Removes the Last Name field from the checkout form.
 * Author: Easy Digital Downloads
 * Author URI: https://easydigitaldownloads.com/
 * Version: 1.0
 */

function pw_edd_remove_last_name_field() {
	remove_action( 'edd_purchase_form_after_user_info', 'edd_user_info_fields' );
	remove_action( 'edd_register_fields_before', 'edd_user_info_fields' );	
}
add_action( 'init', 'pw_edd_remove_last_name_field' );

function pw_edd_user_info_fields() {
	if ( is_user_logged_in() ) :
		$user_data = get_userdata( get_current_user_id() );
	endif;
	?>
	<fieldset id="edd_checkout_user_info">
		<span><legend><?php echo apply_filters( 'edd_checkout_personal_info_text', __( 'Personal Info', 'edd' ) ); ?></legend></span>
		<?php do_action( 'edd_purchase_form_before_email' ); ?>
		<p id="edd-email-wrap">
			<label class="edd-label" for="edd-email">
				<?php _e( 'Email Address', 'edd' ); ?>
				<?php if( edd_field_is_required( 'edd_email' ) ) { ?>
					<span class="edd-required-indicator">*</span>
				<?php } ?>
			</label>
			<span class="edd-description"><?php _e( 'We will send the purchase receipt to this address.', 'edd' ); ?></span>
			<input class="edd-input required" type="email" name="edd_email" placeholder="<?php _e( 'Email address', 'edd' ); ?>" id="edd-email" value="<?php echo is_user_logged_in() ? $user_data->user_email : ''; ?>"/>
		</p>
		<?php do_action( 'edd_purchase_form_after_email' ); ?>
		<p id="edd-first-name-wrap">
			<label class="edd-label" for="edd-first">
				<?php _e( 'First Name', 'edd' ); ?>
				<?php if( edd_field_is_required( 'edd_first' ) ) { ?>
					<span class="edd-required-indicator">*</span>
				<?php } ?>
			</label>
			<span class="edd-description"><?php _e( 'We will use this to personalize your account experience.', 'edd' ); ?></span>
			<input class="edd-input required" type="text" name="edd_first" placeholder="<?php _e( 'First name', 'edd' ); ?>" id="edd-first" value="<?php echo is_user_logged_in() ? $user_data->first_name : ''; ?>"/>
		</p>
		<?php do_action( 'edd_purchase_form_user_info' ); ?>
	</fieldset>
	<?php
}
add_action( 'edd_purchase_form_after_user_info', 'pw_edd_user_info_fields' );
add_action( 'edd_register_fields_before', 'pw_edd_user_info_fields' );
To implement this snippet on your site, create a brand new, empty WordPress plugin and paste the above code inside.