Remove TODO about AUTO and AVM (#3027)

src/write.c

diff --git a/src/write.c b/src/write.c
index b8a87dc..a1106b2 100644
--- a/src/write.c
+++ b/src/write.c
@@ -1546,7 +1546,7 @@
 
 static avifCodecType avifEncoderGetCodecType(const avifEncoder * encoder)
 {
-    // TODO(yguyon): Rework when AVIF_CODEC_CHOICE_AUTO can be AVM
+    // This asserts that images cannot be encoded with AVM unless AVIF_CODEC_CHOICE_AVM is explicitly selected.
     assert((encoder->codecChoice != AVIF_CODEC_CHOICE_AUTO) ||
            (strcmp(avifCodecName(encoder->codecChoice, AVIF_CODEC_FLAG_CAN_ENCODE), "avm") != 0));
     return avifCodecTypeFromChoice(encoder->codecChoice, AVIF_CODEC_FLAG_CAN_ENCODE);