Let's assume we need "clean" strings. Clean means a string should only contain letters `a-z`, `A-Z` and spaces. We assume that there are no double spaces or line breaks.
Write a function that takes a string and returns a string without the unnecessary characters.
### Examples
```python
remove_chars('.tree1')    ==> 'tree'
remove_chars("that's a pie$ce o_f p#ie!")  ==> 'thats a piece of pie'
remove_chars('john.dope@dopington.com')    ==> 'johndopedopingtoncom'
remove_chars('my_list = ["a","b","c"]')    ==> 'mylist  abc'
remove_chars('1 + 1 = 2')    ==> '    ' (string with 4 spaces)
remove_chars("0123456789(.)+,|[]{}=@/~;^$'<>?-!*&:#%_")  ==> '' (empty string)
```
def remove_chars(s):
    letters = "abcdefghijklmnopqrstuvwxyz "
    return "".join([i for i in s if i in letters or i in letters.upper()])
def remove_chars(s):
    letters = "abcdefghijklmnopqrstuvwxyz "
    return "".join([i for i in s if i in letters or i in letters.upper()])