[tz] redundant Rule in proposal for Macao

[Michael H Deckers]

    In Paul Eggert's proposal for Macao from 2018-05-10, we find
       +Rule   Macau   1949    1951    -       Apr     Sat>=1 23:00s  
1:00    D
       +Rule   Macau   1951    only    -       Mar     31 23:00s  1:00    D
    with two successive switches to summer time at 1951-03-31 and 
1951-04-07.

    The later switch has no effect, and can easily be omitted:
       +Rule   Macau   1949    1950    -       Apr     Sat>=1 23:00s  
1:00    D

    There are several similar cases in tzdb where the specification
    contains redundant data. For instance,
       Rule    HK      1965    1976    -       Apr     Sun>=16 3:30    
1:00    S
       Rule    HK      1973    only    -       Dec     30 3:30    1:00    S
    with two successive switches to summer time at 1973-12-30 and 
1974-04-21,
    the latter having no effect. In this case, removal of the redundancy
    would require an addtional Rule line, so concise notation could be
    construed as a reason for retaining the redundancy.

    Do we have a guideline for such cases?

    Michael Deckers.