MAINT: minor cleanup of old version workarounds

[bsipocz]

Trivial PR, but I didn't want to mix these changes into something totally unrelated.

[codecov]

Codecov Report

Merging #453 (1efddf1) into main (c4f67e5) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #453      +/-   ##
==========================================
- Coverage   80.08%   80.08%   -0.01%     
==========================================
  Files          52       52              
  Lines        6021     6020       -1     
==========================================
- Hits         4822     4821       -1     
  Misses       1199     1199              

Impacted Files	Coverage Δ
pyvo/samp.py	34.09% <100.00%> (-1.47%)	⬇️

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[msdemlei]

I trust your call as to that anything that would break on these fallbacks would break on any number of other changes, too, so: go ahead.

[bsipocz]

Yeap, one of these is astropy 2.x-ish, the other is python 3.3, both well within out range. I checked and didn't find another similar and obvious case.