Combine dependencies and dependencies-linux

Platform dependencies aren't supported according to the dub
documentation, that states: "this setting does not support platform
suffixes".

dub test with dub 1.34.0 produces a warning:

"dependencies-linux: Key is not a valid member of this section.
Did you mean: dependencies"

Then the build fails because it cannot find modules defined in the
dependency.

dub.json

@@ -13,10 +13,7 @@
 		"tanya:meta": "*",
 		"tanya:os": "*",
 		"tanya:middle": "*",
-		"tanya:test": "*"
+		"tanya:test": "*",
-	},
-
-	"dependencies-linux": {
 		"mir-linux-kernel": "~>1.0.0"
 	},