Remove random number generation code

[drinkcoffee]

This PR removes the random number generation code from main. The code in main at present has issues and was to be replaced with the code on random2 branch. However, the code in the random2 branch requires the creation of a off-chain service (and has a few small issues). There is currently not sufficient customer demand to create such a service. Hence, this PR:

• Removes all random number generation source code
• Removes all random number generation test code.
• Updates the readme file in the contracts/ random directory to indicate that Immutable has investigated on-chain random, and points customers to the random2 branch, in particular the thread model document.

[openzeppelin-code[bot]]

Remove random number generation code

Generated at commit: 09d0462d2b964e3cc2c8b1ba8a4545f054343f19

🚨 Report Summary

	Severity Level	Results
Contracts	Critical High Medium Low Note Total	2 0 0 11 27 40
Dependencies	Critical High Medium Low Note Total	0 0 0 0 0 0

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