OK, that's it - no callout drivers left, so we drop the warning from
tty_open() and kill the code that handles them in /proc/tty/drivers.

misc cleanup - switched to standard constant names for .subtype in the
drivers that had private equivalents, removed unused ->callout_termios
and friends from the last places where they were defined.

callout removal: isdn

callout removal: cris

callout removal: simserial

callout removal: mips

callout removal: vacserial

callout removal: sicc

callout removal: 8260_uart

callout removal: 8xx_uart

callout removal: amiserial

callout removal: cyclades

callout removal: dz

callout removal: epca

callout removal: esp

callout removal: ip2

callout removal: moxa

callout removal: mxser

callout removal: pcxx

callout removal: rocket

callout removal: serial167

callout removal: synclink

callout removal: synclinkmp

callout removal: synclink_cs

callout removal: macserial

callout removal: pc300

callout removal: chdlc

callout removal: 68328

callout removal: isicom

callout removal: generic_serial

callout removal: tx3912

callout removal: vme

callout removal: sci

callout removal: istallion

callout removal: riscom8

callout removal: a2232

callout removal: specialix

callout removal: sx

callout removal: rio

callout removal: stallion