Update requirements.txt

[JerryChen97]

unpin scipy

Changes: follow #78 to simplify the requirements.txt so that we are free of CodeFactor complaints.

Benefits:

1. Fixing https://app.readthedocs.com/projects/xanaduai-pennylane-aqt/builds/2972169/ which was caused by a super old scipy whose version pinned three years ago.
2. Advanced the needed requirements change there as well.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (4e0236f) to head (b0c9ec8).
Report is 6 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##            master       #87   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            6         6           
  Lines          171       171           
=========================================
  Hits           171       171           

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[andrijapau]

codefactor?

[JerryChen97]

I don't think the CodeFactor complaint on requriements line0 makes any sense...

[andrijapau]

During hackweek i was cleaning up this repo and found that the requirements can be simplified greatly. Try that.

#78

[astralcai]

In this case I wonder if requirements.txt is even needed