Docs: this_cpu_ops: remove redundant add forms

Commit ac490f4dca94 (Documentation: this_cpu_ops.txt: Update description
of this_cpu_ops) added lists of {__,}this_cpu operations, but these have
duplicate, parameter-less entries for {__,}this_cpu_add which don't
correspond to any implementation. No other operations have such
duplicate entries.

Given both are also listed with their full complement of arguments, the
empty forms are redundant and can be removed. This patch performs said
removal.

Signed-off-by: Mark Rutland <[e-mail]>
Reviewed-by: Pranith Kumar <[e-mail]>
Acked-by: Christoph Lameter <[e-mail]>
Signed-off-by: Randy Dunlap <[e-mail]>
Signed-off-by: Jiri Kosina <[e-mail]>

Documentation/this_cpu_ops.txt

···
 are defined. These operations can be used without worrying about
 preemption and interrupts.
 
-	this_cpu_add()
 	this_cpu_read(pcp)
 	this_cpu_write(pcp, val)
 	this_cpu_add(pcp, val)
···
 modifies the variable, then RMW actions can not be guaranteed to be
 safe.
 
-	__this_cpu_add()
 	__this_cpu_read(pcp)
 	__this_cpu_write(pcp, val)
 	__this_cpu_add(pcp, val)