Replace `requests` by `urllib`

[pmeier]

🚀 The feature

See title.

Motivation, pitch

The requests library is currently an optional dependency. It is used only for downloading from GDrive:

vision/torchvision/datasets/utils.py

Lines 193 to 203 in 30f4d10

	def download_file_from_google_drive(file_id: str, root: str, filename: Optional[str] = None, md5: Optional[str] = None):
	"""Download a Google Drive file from and place it in root.
	Args:
	file_id (str): id of file to be downloaded
	root (str): Directory to place downloaded file in
	filename (str, optional): Name to save the file under. If None, use the id of the file.
	md5 (str, optional): MD5 checksum of the download. If None, do not check
	"""
	# Based on https://stackoverflow.com/questions/38511444/python-download-files-from-google-drive-using-url
	import requests

It would be nice to refactor this to use urllib and drop a "hidden" dependency. From skimming the the linked StackOverflow issue, it seems our implementation is almost a 1-to-1 copy. Thus, I'd wager a guess that requests was simply chosen, because the solution was already there and not because the functionality is not available in urllib.

Alternatives

No response

Additional context

See #4917.

cc @pmeier