Disable openCL for appveyor:

[coder3101]

openCL tests on Appveyor are failing due to some vcpkg issue.

As per my mentor @bassoy request, I am removing the openCL tests from the appveyor. The mentioned reason for this removal is:

• We will soon migrate to openMP with new tensor design
• openCL usage is not documented and hence very likely not being used.

[codecov]

Codecov Report

Merging #104 into develop will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop     #104   +/-   ##
========================================
  Coverage    95.33%   95.33%           
========================================
  Files           22       22           
  Lines         1223     1223           
========================================
  Hits          1166     1166           
  Misses          57       57           

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