Windows-only and Linux-only add-ons are flagged as incompatible with Quantum

[kumar303]

Describe the problem and steps to reproduce it:

• Create a windows-only or linux-only extension that supports Firefox 57
• Go to its listing page

What happened?

It says incompatible with Firefox Quantum

What did you expect to happen?

It should not include this badge.

Anything else we should know?

See #5012 for details. Also see this thread: https://discourse.mozilla.org/t/extension-not-compatible-with-firefox-quantum/21460/7

This is a follow-up to #11160

[ValentinaPC]

Verified as fixed on AMO-dev FF56(Win 7).
Only-Win and only-Linux compatible add-ons are not flagged as incomaptible with Quantum.
Examples:

• https://addons-dev.allizom.org/en-US/developers/addon/webext-linux/versions/1533230
  

• https://addons-dev.allizom.org/en-US/firefox/addon/webext-win/