docs: remove spfx docs

[HuihuiWu-Microsoft]

Will add new wiki page for spfx-help-v5 doc and update the aka link(https://aka.ms/teamsfx-spfx-help-v5) later

[yuqizhou77]

might be safer to have the new page ready and update aka.ms link. Then remove old pages.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.40%. Comparing base (63925ea) to head (9fb2633).

Additional details and impacted files

@@           Coverage Diff            @@
##              dev   #11638    +/-   ##
========================================
  Coverage   88.40%   88.40%            
========================================
  Files         536      536            
  Lines       32664    32664            
  Branches     6458     6321   -137     
========================================
  Hits        28876    28876            
  Misses       1843     1843            
  Partials     1945     1945            

[HuihuiWu-Microsoft]

might be safer to have the new page ready and update aka.ms link. Then remove old pages.

Sure, will create the new page once confirmed with PM before merge the PR. Thanks for reminding