Removing CONTRIBUTING file

[erickpintor]

Closes: https://github.com/faunadb/sales-engineering/issues/465

None of our other drivers have this file and it does not reflect how we currently approach contributions.

I feel like we need to come up with something more official and applicable for all drivers. Until then, I prefer to remove this.

[codecov-io]

Current coverage is 94.42% (diff: 100%)

Merging #92 into master will not change coverage

@@             master        #92   diff @@
==========================================
  Files            17         17          
  Lines          1094       1094          
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
==========================================
  Hits           1033       1033          
  Misses           61         61          
  Partials          0          0          

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[eaceaser]

lgtm