Remove pre 0.2.0 deprecation warnings

[tlambert03]

Removing deprecation warnings from the 0.2.0 release, will now be errors in 0.2.7

[codecov]

Codecov Report

Merging #138 (617f02e) into master (cb83f9f) will increase coverage by 0.22%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #138      +/-   ##
==========================================
+ Coverage   90.97%   91.20%   +0.22%     
==========================================
  Files          25       25              
  Lines        2526     2500      -26     
==========================================
- Hits         2298     2280      -18     
+ Misses        228      220       -8     

Impacted Files	Coverage Δ
magicgui/widgets/_bases/container_widget.py	94.90% <ø> (+1.11%)	⬆️
magicgui/widgets/_function_gui.py	96.29% <ø> (-0.31%)	⬇️
magicgui/widgets/_bases/categorical_widget.py	80.64% <100.00%> (+5.99%)	⬆️
magicgui/widgets/_bases/widget.py	87.20% <100.00%> (-0.08%)	⬇️

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[sofroniewn]

LGTM!