DOC: cleaned references to pandas v0.15 and v0.16 in docs

[topper-123]

Last round of cleanup of references to older pandas versions (here v0.15 and v0.16).

I'm not intending to go further up: v0.16.2 was released in june 2015, and allowing up to 2 years old references to be seen in the docs themselves is reasonable IMO. (but other may have a different view, so if there's a "demand" I could change the cut-off point, its not so much work).

See also #17420 and #17404.

I also removed a reference to python 3.4 in the install.rst. In the same document, I also "updated" the test section to show python3.6 (just a (very) minor signal that pandas is python 3 positive).

[codecov]

Codecov Report

Merging #17442 into master will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #17442      +/-   ##
==========================================
- Coverage   91.15%   91.14%   -0.02%     
==========================================
  Files         163      163              
  Lines       49587    49587              
==========================================
- Hits        45203    45194       -9     
- Misses       4384     4393       +9

Flag	Coverage Δ
#multiple	88.92% <ø> (ø)	⬆️
#single	40.25% <ø> (-0.07%)	⬇️

Impacted Files	Coverage Δ
pandas/io/gbq.py	25% <0%> (-58.34%)	⬇️
pandas/core/frame.py	97.72% <0%> (-0.1%)	⬇️

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[jreback]

lgtm. some minor comments. ping when pushed / green.

[jreback]

you can take this out (about older PyTables)

[jreback]

iI would update the pandas & numpy version here as well (you can just change the text) to something more current

[jreback]

actually this is from an older nose run, can you fix up to show what pytest prints.

[jreback]

pls also add a whatsnew entry on Other Enhancements that docs are now updated to remove older references (and you can list the issue / PR's that were involved).

[topper-123]

ping @jreback

[jreback]

thanks @topper-123 very nice series of changes!

when docs are built (could be a while), see http://pandas-docs.github.io/pandas-docs-travis/

and if anything needs corrections pls push a PR.

[topper-123]

Ok, I'll go look in a few days.

Yeah, these 3 commits have a net reduction in line count of ca. 330 lines, that's quite a bit of deadweight removed :-)