Update 2020/2021
As Cameron Cobb pointed out,
Safari Mobile supports the new HTML attribute enterkeyhint since version 13.7 ~ Sept. 2020 (https://caniuse.com/mdn-html_global_attributes_enterkeyhint).
The following values are possible (https://mixable.blog/ux-improvements-enterkeyhint-to-define-action-label-for-the-keyboard-of-mobile-devices/):
<input enterkeyhint="enter">
<input enterkeyhint="done">
<input enterkeyhint="go">
<input enterkeyhint="next">
<input enterkeyhint="previous">
<input enterkeyhint="search">
<input enterkeyhint="send">
Original Answer
Aha…
The ‘Go’ button is only shown, if the <input> tag is inside a <form> tag (and the form tag has an action attribute).
So, if you access your form elements afterwards with i.e. JavaScript, you can omit <form> tags.
‘Go’ button:
<form action="..." method="...">
<input type="text"></input>
</form>
‘return’ button:
<input type="text"></input>
