Don't override server_aliases with short_buffer_names
Don't override server_aliases with short_buffer_names

There's no reason to not use the server aliases even when
short_buffer_names is on. Now, it will use server aliases for the
servers that has it defined, and short names for the rest if
short_buffer_names is on.

wee-slack/wee-slack,trygveaa/wee-slack,rawdigits/wee-slack