Merge Fibonacci files

[tianyizheng02]

As shown by issues #5665 and #5733, there are apparently multiple files for calculating the Fibonacci sequence, namely dynamic_programming/fibonacci.py and maths/fibonacci.py. There's also a third file, maths/fibonacci_sequence_recursion.py, that's not mentioned in the previous issues, and there might be more that I haven't spotted yet. Each of these files provides different algorithms for calculating the sequence.

I feel like some if not all of these files should be combined into one file. It'd not only be more convenient, but it'd also be easier to compare the algorithms against one another.

[tianyizheng02]

I've merged maths/fibonacci.py and maths/fibonacci_sequence_recursion.py, but feel free to contribute if other Fibonacci files need to be merged as well