Here is a GreaseMonkey script I threw together:
// ==UserScript==
// @name Old Comment Delete Button
// @version 1.1.0
// @grant none
// @author a stone arachnid
// @include https://*stackoverflow.com/*
// @include https://*superuser.com/*
// @include https://*serverfault.com/*
// @include https://*stackapps.com/*
// @include https://*askubuntu.com/*
// @include https://*mathoverflow.net/*
// @include https://*stackexchange.com/*
// @exclude http*://*chat.*/
// @require https://gist.githubusercontent.com/BrockA/2625891/raw/9c97aa67ff9c5d56be34a55ad6c18a314e5eb548/waitForKeyElements.js
// ==/UserScript==
(function(){
var styles = `
.js-comment-delete,.js-comment-delete:hover,.js-comment-delete:focus{
margin:0;
line-height:1;
width:14px;
height:14px;
background:rgba(36,39,41,0.25);
border-radius:7px;
box-sizing:border-box;
padding:2px;
color:white!important;
display:none;
}
.comment:hover .js-comment-delete,.js-comment-delete:focus{
display:inline;
}
.js-comment-delete:hover{
background:rgba(36,39,41,0.6);
}
.js-comment-delete:active{
background:rgba(127,0,0,1)!important;
}
.js-comment-delete:focus{
box-shadow:none;
}
`,svg='<svg class="svg-icon va-text-bottom iconClearSm" width="14" height="14" viewBox="0 0 20 20"><path d="M12 3.41L10.59 2 7 5.59 3.41 2 2 3.41 5.59 7 2 10.59 3.41 12 7 8.41 10.59 12 12 10.59 8.41 7z"></path></svg>';
StackExchange.ready(function(){
$("<style></style>").text(styles).appendTo("head");
$(".js-comment-delete").removeClass("fc-red-600").html(svg);
});
waitForKeyElements(".comment",function(jNode){
$(jNode).find(".js-comment-delete").removeClass("fc-red-600").html(svg);
})
})();