nir: Remove stale TODOs

If nobody has added def-use lists for registers in all this time, it's probably
because we don't want them after all ;)

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Reviewed-by: Faith Ekstrand <faith.ekstrand@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/23107>

src/compiler/nir/nir.h

@@ -970,8 +970,6 @@ typedef struct {
    nir_register *reg;
    struct nir_src *indirect; /** < NULL for no indirect offset */
    unsigned base_offset;
-
-   /* TODO use-def chain goes here */
 } nir_reg_src;
 
 typedef struct {
@@ -981,8 +979,6 @@ typedef struct {
    nir_register *reg;
    struct nir_src *indirect; /** < NULL for no indirect offset */
    unsigned base_offset;
-
-   /* TODO def-use chain goes here */
 } nir_reg_dest;
 
 struct nir_if;