[m2sci] kernel code reorganization: clarify dependencies & ease code browsing

[m2sci] kernel code reorganization: clarify dependencies & ease code browsing

  test_run("m2sci",[],"enable_lt")  // (no new failing tests)

  No code content changed.

  * changevarname() never called => DELETED
    old2newinstr() called only only in changevarname() => DELETED

  * Minor functions called within a single other one are transfered as
    private functions:
    ("A=>B" means "A() called only in B(), and so transfered into B.sci")
    get_unknown    => in getvar2sci
    default_trad   => in funcall2sci
       mtlbtoolfun => default_trad => funcall2sci
    transformtree  => mfile2sci
    multi_fun_file => mfile2sci
    infer2txt      => m2sci
    translateorder => translatepath
    variablesearch => lst_funcall
    funcallsearch  => lst_funcall
    get_unknown    => getvar2sci
    equal2sci      => instruction2sci
    clause2sci     => instruction2sci
    updatevarslist => (equal2sci, clause2sci) => instruction2sci
    i_notation     => m2sci_syntax
    replace_brackets   => syntax_m2sci
    replace_end_dollar => syntax_m2sci

   * Bigger functions called in a single one: left apart as public
     + dependency info added in their heading comment
      m2sci:            called only in mfile2sci()
      lst_funcall:      called only in translatepath()
      sci_m2scideclare: called only in expression2sci()
      funcall2sci:      called only in expression2sci()
      mtlbtoolfun:      called only in default_trad()

Change-Id: Ic444781ac118902253ee88386ffb195073acf3f4