[clang][docs] Remove reference to deleted line in sanitizer doc (llvm#141921)

This was added by 8eb3470 which added
an opt into the new ignore list behaviour.

Then 81d1df2 flipped it so you had to
opt into the old behaviour, but didn't remove the "The line above" bit.

Author: DavidSpickett

clang/docs/SanitizerSpecialCaseList.rst

@@ -156,7 +156,6 @@ tool-specific docs.
 
 .. code-block:: bash
 
-    # The line above is explained in the note above
     # Lines starting with # are ignored.
     # Turn off checks for the source file
     # Entries without sections are placed into [*] and apply to all sanitizers