chore: remove 3.4 deprecation

[maxhelias]

Q	A
Branch?	4.1
Tickets	-
License	MIT
Doc PR	-

This must be the last deprecation :

• Remove GraphQL Playground
• Remove phpdocumentor/reflection-docblock in favor of phpstan/phpdoc-parser

[soyuka]

should we target main instead for these? I'm not sure we cover the bc on every parameters that get removed in this patch

[maxhelias]

I think that apart from what concerns the json format for OpenAPI (which breaks the tests btw), the rest can stay in 4.1.
I can extract what concerns OpenAPI in another PR to main and keep the rest here for 4.1. WDYT ?

[soyuka]

yes this would be perfect! Also could you point me to why we remove the graphql-playground ?

[maxhelias]

To keep only GraphiQL : #5309

[soyuka]

Thanks a lot @maxhelias !