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Just Login with your details and go to, https://m.facebook.com/friends/c...
which will display all your pending sent requests. Open "Inspect" by Right click on the same page now go to "console" in top tabs and hit below script.
javascript:var inputs = document.getElementsByClassName('_54k8 _56bs _56bt');
for(var i=0; i inputs[i].click();}
That's all, all your requests open on that page will be deleted.