Fixed no-else-return message in probnum.linalg module

[peterw2333]

In a Nutshell

Fixed no-else-return message in probnum.linalg module

Detailed Description

Removes unnecessary else after return, and changing unneccessary elif after return to if.
pylint no-else-return(R1705)

Related Issues

Finishes objective 2 in #671

[codecov]

Codecov Report

Merging #699 (3aecd05) into main (cb5b55a) will not change coverage.
The diff coverage is 70.58%.

@@           Coverage Diff           @@
##             main     #699   +/-   ##
=======================================
  Coverage   90.02%   90.02%           
=======================================
  Files         194      194           
  Lines        7350     7350           
  Branches     1161     1161           
=======================================
  Hits         6617     6617           
  Misses        489      489           
  Partials      244      244           

Impacted Files	Coverage Δ
src/probnum/linalg/solvers/matrixbased.py	73.75% <37.50%> (ø)
...um/linalg/solvers/beliefs/_linear_system_belief.py	91.42% <100.00%> (ø)
...num/linalg/solvers/policies/_conjugate_gradient.py	91.42% <100.00%> (ø)

[JonathanWenger]

Looks good, thanks!