Remove some dead functions from uvm.9:

uvm_fork() was removed by uvm_glue.c r1.65 (2014-05-15)

uvm_scheduler() was removed by uvm_glue.c r1.50 (2009-08-11)

uvm_swapin() was removed by uvm_glue.c r1.45 (2006-11-29)

RIP