http_session: don't disable InsecureRequestWarning

[bastimeyer]

ref #4523 (comment)

InsecureRequestWarning can be emitted by urllib3 here:
https://github.com/urllib3/urllib3/blob/1.26.9/src/urllib3/connectionpool.py#L1042-L1062

---

Example with HTTPS requests on a temporarily set up TLS certificate that's self-signed:

Without --http-no-ssl-verify (SSLCertVerificationError):

$ streamlink httpstream://https://test.bastimeyer.de/test.mp4 best
[cli][info] Found matching plugin http for URL httpstream://https://test.bastimeyer.de/test.mp4
[cli][info] Available streams: live (worst, best)
[cli][info] Opening stream: live (http)
[cli][info] Starting player: mpv
[cli][error] Try 1/1: Could not open stream <HTTPStream('https://test.bastimeyer.de/test.mp4')> (Could not open stream: Unable to open URL: https://test.bastimeyer.de/test.mp4 (HTTPSConnectionPool(host='test.bastimeyer.de', port=443): Max retries exceeded with url: /test.mp4 (Caused by SSLError(SSLCertVerificationError(1, '[SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed: self signed certificate (_ssl.c:997)')))))
error: Could not open stream <HTTPStream('https://test.bastimeyer.de/test.mp4')>, tried 1 times, exiting

With --http-no-ssl-verify:

$ streamlink httpstream://https://test.bastimeyer.de/test.mp4 best --http-no-ssl-verify
[cli][info] Found matching plugin http for URL httpstream://https://test.bastimeyer.de/test.mp4
[cli][info] Available streams: live (worst, best)
[cli][info] Opening stream: live (http)
[cli][info] Starting player: mpv
/home/basti/venv/streamlink-310/lib/python3.10/site-packages/urllib3/connectionpool.py:1043: InsecureRequestWarning: Unverified HTTPS request is being made to host 'test.bastimeyer.de'. Adding certificate verification is strongly advised. See: https://urllib3.readthedocs.io/en/1.26.x/advanced-usage.html#ssl-warnings
  warnings.warn(
[cli][info] Stream ended
[cli][info] Closing currently open stream...