Delete panicln from the spec.

R=rsc, gri, iant, ken2
CC=golang-dev
https://golang.org/cl/738041

doc/go_spec.html

@@ -1547,7 +1547,7 @@ Zero value:
 
 Functions:
 	cap close closed cmplx copy imag len make
-	new panic panicln print println real
+	new panic print println real
 </pre>
 
 
@@ -4525,7 +4525,6 @@ Function   Behavior
 print      prints all arguments; formatting of arguments is implementation-specific
 println    like print but prints spaces between arguments and a newline at the end
 panic      like print, aborts execution after printing
-panicln    like println, aborts execution after printing
 </pre>