Remove obsolete strings from the download page resource

[chrisgarrity]

When we were getting ready to release the Scratch android app we had two versions of the download page. Now that the app has been released, the obsolete strings should be removed so that we are not making unnecessary work for translators.

It would be good to check that all the strings in https://github.com/LLK/scratch-www/blob/develop/src/views/download/l10n.json are still in use in the view.

At the very least the ChromeOS support Q&A is not used: https://github.com/LLK/scratch-www/blob/90a132477f63167e7a7b92c25060e90270db6270/src/views/download/l10n.json#L13-L14

Other things to look for - any strings that use "Desktop" as we standardized on "app" for all the standalone applications. E.g. there are two versions of this answer: https://github.com/LLK/scratch-www/blob/90a132477f63167e7a7b92c25060e90270db6270/src/views/download/l10n.json#L33-L34

[apple502j]

List of unused strings:

• download.startScratchDesktop
• download.howDoIInstall
• download.whenSupportLinux
• download.supportLinuxAnswer
• download.supportChromeOS
• download.supportChromeOSAnswer
• download.cannotAccessMacStore
• download.cannotAccessWindowsStore
• download.macMoveToApplications
• download.canIUseScratchLink
• download.canIUseScratchLinkAnswer
• download.canIUseExtensions
• download.canIUseExtensionsAnswer
• download.desktopAndBrowser
• download.canIShare
• download.canIShareAnswer

Other notes:

• download.howConnectHardwareDevicesAnswerLink is inaccurate; as of 3.14.0 it supports Scratch Link without Internet connection.