Removed Python 3.6 subport of py-readline

[radarhere (Andrew Murray)]

#53243 added Python 3.6 to py-readline. However, as noted in that issue, it currently crashes in that environment. So this change removes the subport.

[mf2k (Frank Schima)]

Cc reporter of duplicate #53409.

[akkornel (A. Karl Kornel)]

I hit this issue, and found that installing python36 +readline (after removing py36-readline) got things working again. That made me wonder:

• python36 is still telling people to install py36-readline if using Python from the Terminal. Should that be changed to reference the readline variant?
• Should the readline variant be marked as default? Or is there a way to get python36+readline to be cached at Macports even though it's not the default?

I ask the latter question because it may be annoying to users who install Python 3.6, only to be told that they have to re-install (with the extra build delay) what they just installed, if they wanted to use the Terminal.

[JDLH (Jim DeLaHunt)]

This problem occurred for me also.

Uninstalling py36-readline, then doing sudo port install python36 +readline fixed the crash for me.

For the benefit of others searching for a solution to this problem, I'm pasting the crash symptoms here:

% python3.6
Python 3.6.0 (default, Dec 23 2016, 12:50:55) 
[GCC 4.2.1 Compatible Apple LLVM 8.0.0 (clang-800.0.38)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> a=2
Python(26362,0x7fffab1043c0) malloc: *** error for object 0x108253640: pointer being freed was not allocated
*** set a breakpoint in malloc_error_break to debug
Abort trap: 6

I strongly agree that we should improve the notes for python36. Here's what they just told me. As best I understand, this is bad advice. It should instead say, "If you are using python36 from the terminal, install python36 +readline . Uninstall py36-readline, it is not necessary for python36 and later."

  python36 has the following notes:
    To make this the default Python or Python 3 (i.e., the version run by the 'python' or 'python3' commands), run one or both of:
    
        sudo port select --set python python36
        sudo port select --set python3 python36
    
    ##############################################################
    # IF YOU ARE USING PYTHON FROM THE TERMINAL, PLEASE INSTALL:
    #   py36-readline
    # TO AVOID A LIBEDIT / PYTHON INTERACTION ISSUE.
    # REF: https://trac.macports.org/ticket/48807
    ##############################################################

[mf2k (Frank Schima)]

Has duplicate #54185.

[petrrr]

Assigning this to the maintainer of python36, because of the discussion on notes and variant.

[raimue (Rainer Müller)]

Why not fix the crash by backporting the upstream fix instead of removing support? According to the ​upstream report, the latest master works.

[ryandesign (Ryan Carsten Schmidt)]

py-readline needs to be replaced with py-gnureadline; see #44206. But py-gnureadline needs to be fixed for this problem. It's unclear to me just based on looking at the commits which commit would fix this problem.

[jmroot (Joshua Root)]

See also #53176.

[jmroot (Joshua Root)]

In 2185280a3817ff020fc64fd09cea871618a8b8ba/macports-ports:

py-readline, py-gnureadline: remove broken py36 subport

Closes: #53360