[FIX] point_of_sale: Black background receipts

Some receipts still had part of their backgrounds black.

addons/point_of_sale/static/src/css/pos_receipts.css

@@ -1,6 +1,4 @@
 .pos-receipt-print {
-    /*The receipt must be in the top left corner when rendered by html2canvas*/
-    margin: -8px;
     width: 512px;
     text-align: left;
     direction: ltr;

addons/point_of_sale/static/src/js/printers.js

@@ -46,23 +46,11 @@ var PrinterMixin = {
      */
     htmlToImg: function (receipt) {
         var self = this;
-        $('.pos-receipts').html(receipt);
-        $('.pos-receipts>.pos-receipt').addClass('pos-receipt-print');
+        $('.pos-receipt-print').html(receipt);
         var promise = new Promise(function (resolve, reject) {
             html2canvas($('.pos-receipt-print')[0], {
-                background :'#FFFFFF',
-                height: $('.pos-receipt-print').outerHeight(),
-                ignoreElements: function (node) {
-                    // By default, html2canvas copies the whole DOM even if we just capture a part
-                    // of it. When copying the list of products, it gets all of the product from the
-                    // backend. We ignore the content of <div class="pos"> to speed things up.
-                    if (node.className == "pos") {
-                        return true;
-                    }
-                    return false;
-                },
                 onrendered: function (canvas) {
-                    $('.pos-receipts').empty();
+                    $('.pos-receipt-print').empty();
                     resolve(self.process_canvas(canvas));
                 } 
             })

addons/point_of_sale/static/src/xml/pos.xml

@@ -2,7 +2,7 @@
 <templates id="template" xml:space="preserve">
 
     <t t-name="Chrome">
-        <div class='pos-receipts'>
+        <div class='pos-receipt-print'>
             <!-- here go the receipts that will be printed -->
         </div>