Remove start-up scripts for Unicorn web server

What does this MR do?

This is split from bigger Unicorn removal MR: !61888 (merged)

We try to move in small steps, so this MR only addresses binaries and init.d config.
I also replaced bin/web by bin/web_puma, the diff may look dirty, but it was mv bin/web_puma bin/web.

lib/gitlab/cluster/lifecycle_events.rb, lib/gitlab/runtime.rb, lib/prometheus/pid_provider.rb and other Ruby layer stuff will addressed in the next MR(s).

Not 100% sure if a changelog is needed though.

Does this MR meet the acceptance criteria?

Conformity

• I have included a changelog entry, or it's not needed. (Does this MR need a changelog?)
• I have added/updated documentation, or it's not needed. (Is documentation required?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request perormance guidelines)
• I have followed the style guides.

Availability and Testing

I didn't find any great ways to test it locally, grepped for usage, and did gdk start, gdk stop, gdk restart which hits bin/web binary.
Confirmed that by putting echo into bin/web (which appeared in gdk tail).

Security

N/A

Related to #330402 (closed)