Remove flush_all from docs

[kpp]

rust-libp2p/core/src/muxing.rs

Line 68 in cb3784a

/// - A connection to the remote. The `poll_event`, `flush_all` and `close` methods operate

Because the method was removed in #2669

cc @thomaseizinger

[thomaseizinger]

Thanks! That was indeed an oversight.

The docs will re-worked here: https://github.com/libp2p/rust-libp2p/pull/2707/files#diff-1d8f8fba36155ce3fd2849bc74180b4aa5399051838235c3dcbd5b99b8ed908eR64-R71

I'll attach this issue as being fixed with #2707.