sshfs_mount: remove Process.kill() on failed mount

With [1] we needed to figure out a solution for Windows that was
different than for Linux. After doing some testing I have found
that we don't really need the Process.kill() calls; even without
it, the processes on Windows/Mac/Linux get cleaned up properly if
the mount fails.

Fixes #21

[1] #21

lib/vagrant-sshfs/cap/linux/sshfs_mount.rb

@@ -171,8 +171,6 @@ def self.sshfs_slave_mount(machine, opts, hostpath, expanded_guest_path)
             sleep(2)
           end
           if !mounted
-            Process.kill("TERM", p1) 
-            Process.kill("TERM", p2) 
             raise VagrantPlugins::SyncedFolderSSHFS::Errors::SSHFSSlaveMountFailed
           end
           machine.ui.info("Folder Successfully Mounted!")