xcbgen: Various small fixes for SwitchType

The calc_size() method is removed because there is no need to override
it (the superclass resolve method isn't called).

Signed-off-by: Ran Benita <ran234@gmail.com>
xcbgen: Spell out the names of make_member_of() arguments

Spelling out the argument names explicitly makes it easier to see what's
going on at a glance. With a bunch of True and False you need to jump
around.

Signed-off-by: Ran Benita <ran234@gmail.com>
xcbgen: Remove trailing whitespace

(and one typo).

Signed-off-by: Ran Benita <ran234@gmail.com>
xcbgen: Remove unneeded BitcaseType _placeholder_byte code

A _placeholder_byte is never added to a SwitchType's bitcases array, and
the conditioned code is indeed never triggered by any XML file.

Signed-off-by: Ran Benita <ran234@gmail.com>
xcbgen: Remove unneeded SwitchType _placeholder_byte code

No one ever adds a _placeholder_byte to a switch (only to request,
reply, event etc.) so the conditioned code is never reached.

Signed-off-by: Ran Benita <ran234@gmail.com>