Remove deprecated serverChannel implementations

[yannbf]

serverChannel:

storybook/code/lib/preview-api/src/modules/addons/main.ts

Line 18 in f78038b

private serverChannel: Channel | undefined;

setServerChannel:

storybook/code/lib/preview-api/src/modules/addons/main.ts

Line 63 in f78038b

setServerChannel = (channel: Channel): void => {

hasServerChannel:

storybook/code/lib/preview-api/src/modules/addons/main.ts

Line 53 in f78038b

hasServerChannel = (): boolean => !!this.serverChannel;

getServerChannel:

storybook/code/lib/preview-api/src/modules/addons/main.ts

Line 38 in f78038b

getServerChannel = (): Channel => {

Seems like this change is going to be a little more involved, so here's the PR that introduced it for more context: #22940

[shilman]

Cc @ndelangen

[ndelangen]

I'm fairly sure, nothing uses these methods anymore, so it's likely fine to remove them?