Remove `ensure_on_device` function

[bwohlberg]

Remove ensure_on_device function. Resolves #451.

[codecov[bot]]

Codecov Report

Merging #463 (a5fb2fd) into main (d0e6c4c) will decrease coverage by 0.03%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #463      +/-   ##
==========================================
- Coverage   94.59%   94.56%   -0.03%     
==========================================
  Files          87       87              
  Lines        5523     5495      -28     
==========================================
- Hits         5224     5196      -28     
  Misses        299      299              

Flag	Coverage Δ
unittests	94.56% <100.00%> (-0.03%)	:arrow_down:

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
scico/linop/_convolve.py	85.56% <100.00%> (-0.76%)	:arrow_down:
scico/linop/_diag.py	97.62% <100.00%> (ø)
scico/linop/_matrix.py	95.97% <100.00%> (ø)
scico/linop/abel.py	98.21% <100.00%> (ø)
scico/linop/optics.py	99.19% <100.00%> (-0.01%)	:arrow_down:
scico/linop/radon_svmbir.py	82.20% <100.00%> (ø)
scico/loss.py	94.83% <100.00%> (-0.12%)	:arrow_down:
scico/numpy/util.py	97.47% <ø> (-0.28%)	:arrow_down:
scico/optimize/_admm.py	95.96% <100.00%> (-0.04%)	:arrow_down:
scico/optimize/_admmaux.py	96.77% <100.00%> (-0.03%)	:arrow_down:
... and 4 more