ash: remove a tentative TODO, it's a wrong idea

Upstream tried it, and then reverted by:

    From: Herbert Xu <herbert@gondor.apana.org.au>
    Date: Tue, 26 May 2020 23:19:05 +1000
    parser: Fix double-backslash nl in old-style command sub

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

shell/ash.c

@@ -12811,7 +12811,7 @@ parsebackq: {
 				goto done;
 
 			case '\\':
-				pc = pgetc(); /* or pgetc_eatbnl()? why (example)? */
+				pc = pgetc(); /* not pgetc_eatbnl! */
 				if (pc != '\\' && pc != '`' && pc != '$'
 				 && (!synstack->dblquote || pc != '"')
 				) {