JavaScript (ES6), 74 bytes
#JavaScript (ES6), 74 bytes I'mI'm sure there's a shorter way to do this!
s=>[...Array(95)].map((_,y)=>s.includes(c=String.fromCharCode(y+32))?"":c) ##Try it
Try it
let f= s=>[...Array(95)].map((_,y)=>s.includes(c=String.fromCharCode(y+32))?"":c) oninput=_=>o.innerText=f(i.value).join`` o.innerText=f(i.value="Hello, World!").join`` <input id=i><pre id=o>