Remove bad generic sqrt method

[fingolfin]

Method dispatch does not take keyword arguments into account. Therefore the kind of dispatch used by this method is risky and can result in an infinite recursion.

Discovered while looking at test failures in PR #2051

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.38%. Comparing base (9e2da0e) to head (31ee918).
Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2068      +/-   ##
==========================================
+ Coverage   88.37%   88.38%   +0.01%     
==========================================
  Files         125      125              
  Lines       31585    31580       -5     
==========================================
- Hits        27913    27912       -1     
+ Misses       3672     3668       -4     

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[lgoettgens]

This changes a StackOverflowError to a MethodError for the cases that dispatched to this method, so IMO a clear improvement (and non-breaking as it just replaces on error by another one)