Wemake-python-styleguide: Method `given_function_called` should only take the function name into account.

[Jrryy]

Bug report

What's wrong

The method given_function_called(node: ast.Call, to_check: Container[str]) -> str in logic.tree.functions is described as a method that returns the name of the function being called in node, in case it is included in to_check. For example:
```python

Let's imagine we are visiting the Call node in print(123, 456) stored in node

called_function = given_function_called(node, ['print'])
print(called_function)

Prints print

But, if we are visiting datetime.timedelta(days=1)

called_function = given_function_called(node, ['timedelta'])
print(called_function)

Prints an empty string, as if timedelta had not been called. The way for it to be shown is:

called_function = given_function_called(node, ['datetime.timedelta'])
print(called_function)

Prints datetime.timedelta

This is related to https://github.com/wemake-services/wemake-python-styleguide/pull/1676#discussion_r508471791

## How is that should be

```python
# If we are visiting `datetime.timedelta(days=1)`
called_function = given_function_called(node, ['timedelta'])
print(called_function)
# Prints `timedelta`

[Jrryy]

Ofc I will be doing this since it is blocking my own PR.

[sobolevn]

We need both. Sometimes we are interested in attributes as well.

[Jrryy]

I understand. I will not change the functionality of this method, but make a different one for this purpose instead.