Use condensed syntax modules in protocol

There is a difference between the error-monad syntax modules of the shell and the protocol. Specifically,

• in the shell:

  module Result_syntax : sig
    …
    val fail : 'error -> ('a, 'error) result
    val tzfail : error -> 'a tzresult (* = ('a, error tztrace) result *)
    …
  end

• in the protocol:

  module Result_syntax : sig
    …
    val fail : 'error -> ('a, 'error) result
    …
  end
  module Tzresult_syntax : sig
    …
    val fail : error -> 'a tzresult (* = ('a, error tztrace) result *)
    …
  end

This MR aligns the syntax modules of the protocol to the ones of the shell.