Documentation cleanup for mark_function_escape.

Author: atrick

docs/SIL.rst

@@ -3842,7 +3842,7 @@ mark_function_escape
 
   sil-instruction ::= 'mark_function_escape' sil-operand (',' sil-operand)
 
-  %2 = mark_function_escape %1 : $*T
+  mark_function_escape %1 : $*T
 
 Indicates that a function definition closes over a symbolic memory location.
 This instruction is variadic, and all of its operands must be addresses.