[Bug] In 2.78.x PDF Footer search box appear when search is enable in docfx.json

**Describe the bug**
In my **docfx.json** file
```
"pdfCoverPage":"./pdf/cover.html",
"pdfFooterTemplate":"./pdf/footer.html"
```

**To Reproduce**
Steps to reproduce the behavior:
1. **pdfFooterTemplate** content
```

```
3. **Build** the site with **docfx 2.78.1**
pdf file have a searchbox on the footer


The cover page works but not the **footer**.
I was able to add image

1. **pdfFooterTemplate** content
```

@media print {
@page {
margin: 0 !important;
}

body {
-webkit-print-color-adjust: exact;
-moz-print-color-adjust: exact;
-ms-print-color-adjust: exact;
print-color-adjust: exact;
}
}