Remove a resolved TODO.

Signed-off-by: Daira Hopwood <daira@jacaranda.org>

protocol/protocol.tex

@@ -10739,7 +10739,6 @@ This can be implemented in one constraint:
 
 \begin{pnotes}
   \item The bit length $n$ is not limited by the field element size.
-
   \item Since the constraint has only a trivial multiplication, it is
         possible to eliminate it by merging it into the boolean constraint
         of one of the output bits, expressing that bit as a linear
@@ -10748,9 +10747,6 @@ This can be implemented in one constraint:
         of the circuit implementation (for a saving of only one constraint
         per unpacking operation), and so we do not use it for the
         \Sapling circuit.
-        \todo{Do we want to use it internally to the BLAKE2s implementation
-        where modularity is not significantly affected?}
-
   \item In the case $n = 255$, for $a < 2^{255} - \ParamS{r}$ there are two
         possible representations of $a \typecolon \GF{\ParamS{r}}$ as a
         sequence of $255$ bits, corresponding to $\ItoLEBSPOf{255}{a}$ and