fix: Remove document on go back click on step 1 (#910)

⭐ Fixes #903 
⭐ Invoke `onBackStep` on "Go Back" click and conditionally render
Go back label string.

apps/marketing/src/app/(marketing)/singleplayer/client.tsx

@@ -248,6 +248,7 @@ export const SinglePlayerClient = () => {
                   recipients={uploadedFile ? [placeholderRecipient] : []}
                   fields={fields}
                   onSubmit={onFieldsSubmit}
+                  canGoBack={true}
                   isDocumentPdfLoaded={true}
                 />
               </fieldset>