Rustfmt ~10 or less line methods in ChannelManager

rustfmt::skips were added recently all over channelmanager in order for
formatting to be enforced for all new code added to the file.

Here we remove a bunch of those skips that aren't necessary because the
methods that are skipped are so short.

Does not include cfg(splicing) code.

Here we just remove the rustfmt skips, in the next commit we'll clean up the
code that rustfmt made too vertical.

Author: valentinewallace