Fixed Linux update mechanism never finishing

[Hainish]

Test plan

1. Launch Brave on Linux (Ubuntu, Fedora)
2. Click the kabob menu and mouse over "Help"
3. Submenu will open up. It should NOT have "Check for Updates..."

Original issue description

Probably b/c Linux stable isn't out yet, I'm guessing?

I'm left with:

Log:

2016-01-29T00:31:27.664Z - platformBaseUrl = https://brave-laptop-updates.global.ssl.fastly.net/1/releases/undefined/0.7.9
2016-01-29T00:31:27.666Z - updateUrl = https://brave-download.global.ssl.fastly.net/releases/winx64
2016-01-29T00:33:27.695Z - checkForUpdates
2016-01-29T00:33:27.696Z - lastCheckTimestamp = 0
2016-01-29T00:33:27.696Z - secondsSinceLastCheck = 0
2016-01-29T00:33:27.697Z - https://brave-laptop-updates.global.ssl.fastly.net/1/releases/undefined/0.7.9?daily=true&weekly=false&monthly=false
2016-01-29T00:33:28.113Z - Metadata: {"statusCode":400,"error":"Bad Request","message":"child \"platform\" fails because [\"platform\" must be one of [winx64, osx]]","validation":{"source":"params","keys":["platform"]}}
2016-01-29T00:39:38.978Z - Already checking for updates...

[bbondy]

There's no update channel for linux based platforms right now, so I guess we should disable the update code for now for this? @diracdeltas thoughts? We could also alternatively do x64 binaries but not sure if they would be compatible everywhere.

[diracdeltas]

disabling for now or just disabling the "check for updates" button seems fine

[luixxiul]

We have already the update channel for linux, right? Closing.

[bbondy]

Right now Linux users need to manual update, but we do need to remove the update UI for Linux.

[luixxiul]

Ah I see. As I saw the following on debian after manual update check, I just thought autoupdate had been implemented.

2016-05-14T17:10:25.512Z - checkForUpdates
2016-05-14T17:10:25.545Z - lastCheckYMD = 2016-05-15
2016-05-14T17:10:25.568Z - lastCheckWOY = 19
2016-05-14T17:10:25.628Z - firstCheckMade = true
2016-05-14T17:10:25.593Z - lastCheckMonth = 5
2016-05-14T17:10:25.628Z - https://brave-laptop-updates.global.ssl.fastly.net/1/releases/dev/0.9.6/undefined?daily=false&weekly=false&monthly=false&first=false
2016-05-14T17:10:27.298Z - update not available

[bsclifton]

Resolved with 9811351