sshfs_reverse_mount: fixup botched copy/paste

In 3b493c1 we made a fix but didn't apply it properly to
the darwin/sshfs_reverse_mount.rb file. Let's fix that here.

lib/vagrant-sshfs/cap/host/darwin/sshfs_reverse_mount.rb

@@ -68,10 +68,8 @@ def self.sshfs_mount(machine, opts)
           opts[:ssh_opts]+= ' -o ServerAliveInterval=30 '  # send keepalives
 
           # SSH connection options
-          # Note the backslash escapes for IdentityFile - handles spaces in key path
           ssh_opts = opts[:ssh_opts]
           ssh_opts+= ' -o Port=' + machine.ssh_info[:port].to_s
-          ssh_opts+= ' -o "IdentityFile=\"' + machine.ssh_info[:private_key_path][0] + '\""'
           ssh_opts+= ' -o UserKnownHostsFile=/dev/null '
           ssh_opts+= ' -F /dev/null ' # Don't pick up options from user's config
           if machine.ssh_info.key?(:private_key_path) and