Revert "Android: add host destination to the workspace" (#2811)

Instead, use #2797, which made the SDK path optional, and simply pass nil by
default as on linux.

Author: finagolfin

Sources/Workspace/Destination.swift

@@ -130,15 +130,6 @@ public struct Destination: Encodable, Equatable {
             extraSwiftCFlags: extraSwiftCFlags,
             extraCPPFlags: ["-lc++"]
         )
-      #elseif os(Android)
-        return Destination(
-            target: nil,
-            sdk: AbsolutePath(ProcessEnv.vars["PREFIX"]!).parentDirectory,
-            binDir: binDir,
-            extraCCFlags: ["-fPIC"],
-            extraSwiftCFlags: [],
-            extraCPPFlags: ["-lstdc++"]
-        )
       #else
         return Destination(
             target: nil,