libaom: remove references to yuv440p pixfmt

Support for it was apparently never in the codebase, and the enum
values were recently removed from the public headers [1]

Fixes build with latest libaom build.

[1] https://aomedia.googlesource.com/aom/+/2e3cd5c5c30fa02134681cda900c32486807af3fSigned-off-by: James Almer <jamrial@gmail.com>

libavcodec/libaom.c

@@ -68,8 +68,6 @@ enum AVPixelFormat ff_aom_imgfmt_to_pixfmt(aom_img_fmt_t img, int depth)
         return AV_PIX_FMT_YUV444P;
     case AOM_IMG_FMT_444A:
         return AV_PIX_FMT_YUVA444P;
-    case AOM_IMG_FMT_I440:
-        return AV_PIX_FMT_YUV440P;
     HIGH_DEPTH(420)
     HIGH_DEPTH(422)
     HIGH_DEPTH(444)
@@ -113,8 +111,6 @@ aom_img_fmt_t ff_aom_pixfmt_to_imgfmt(enum AVPixelFormat pix)
         return AOM_IMG_FMT_I444;
     case AV_PIX_FMT_YUVA444P:
         return AOM_IMG_FMT_444A;
-    case AV_PIX_FMT_YUV440P:
-        return AOM_IMG_FMT_I440;
     case AV_PIX_FMT_YUV420P10:
         return AOM_IMG_FMT_I42016;
     case AV_PIX_FMT_YUV422P10: