To Turn Off Icon on Hover Effect on Divi Contact Form Submit Button add the following css to your Divi->Theme Options->General Panel->Custom Css

.et_pb_contact .et_pb_contact_submit.et_pb_button:after {
display: none;
}
.et_pb_contact .et_pb_contact_submit.et_pb_button:hover {
padding: 0.3em 1em !important
}