Remove falsy dict.get() fallback in `if` statements

```py
# bad
if dct.get(key, False):
if dct.get(key, ""):
if dct.get(key, []):
if dct.get(key, {}):

# good
if dct.get(key):

# bad
if dct.get(key, set()) and other_cond:
if dct.get(key, 0) or other_cond:

# good
if dct.get(key) and other_cond:
if dct.get(key) or other_cond:
```