http2 - set writable = false when closed = true

[ronag]

h2 compat "should" make sure writable === false when closed === true. Though this might cause problems related to 8589c70.

[benjamingr]

@nodejs/http2

[jasnell]

Ping @mcollina

[ronag]

Not sure if closed is even useful here? Though it might be if we merge #15526.

[mcollina]

IMHO we should remove closed from http2 compat.

[apapirovski]

Forgot to add this as "Fixed" note for https://github.com/nodejs/node/pull/15702/files (closed was removed, writable has to stay as is for h1 compatibility)

Could someone close?