Http1 removetx 5921 v11

[catenacyber]

#416 with resistance to having the last (but not first) transaction being freed : popping it, instead of replacing it by NULL, so that we can still use its index

[victorjulien]

I get a Suricata SV failure with this:

===> http-sticky-server: Sub test #1: FAIL : expected 28 matches; got 26 for filter {'count': 28, 'match': {'event_type': 'alert', 'alert.signature_id': 2}}

[victorjulien]

see https://github.com/OISF/suricata/actions/runs/8802614064

[catenacyber]

Continued in #423