remove redundant question marks for channel update params

[donaldchen]

Because the JSON fields for the channel update payload are all optional, either all of the fields or none of the fields in the table should have the ? which indicates optionality. I chose to remove the ? for all of them, so developers can refer to this highlighted part of the doc as the source of truth.

[Misha-133]

This PR also removes ? indicating nullable fields, not optional. It is a different thing and should not be changed. https://discord.com/developers/docs/reference#nullable-and-optional-resource-fields

[donaldchen]

This PR also removes ? indicating nullable fields, not optional. It is a different thing and should not be changed. https://discord.com/developers/docs/reference#nullable-and-optional-resource-fields

Good catch! I'll update that