Use comparison results as avifBool values directly (#107)

Omit the explicit uses of AVIF_TRUE and AVIF_FALSE to convert comparison
results to avifBool.

src/avif.c

diff --git a/src/avif.c b/src/avif.c
index e7918cb..1269f7b 100644
--- a/src/avif.c
+++ b/src/avif.c
@@ -359,10 +359,7 @@
 
 avifBool avifRGBFormatHasAlpha(avifRGBFormat format)
 {
-    if ((format == AVIF_RGB_FORMAT_RGB) || (format == AVIF_RGB_FORMAT_BGR)) {
-        return AVIF_FALSE;
-    }
-    return AVIF_TRUE;
+    return (format != AVIF_RGB_FORMAT_RGB) && (format != AVIF_RGB_FORMAT_BGR);
 }
 
 uint32_t avifRGBFormatChannelCount(avifRGBFormat format)

src/read.c

diff --git a/src/read.c b/src/read.c
index 245c229..d1605b5 100644
--- a/src/read.c
+++ b/src/read.c
@@ -566,8 +566,7 @@
     avifProfileFormat tileProfile = firstTile->image->profileFormat;
     avifNclxColorProfile * tileNCLX = &firstTile->image->nclx;
     avifRange tileRange = firstTile->image->yuvRange;
-    avifBool tileUVPresent = (firstTile->image->yuvPlanes[AVIF_CHAN_U] && firstTile->image->yuvPlanes[AVIF_CHAN_V]) ? AVIF_TRUE
-                                                                                                                    : AVIF_FALSE;
+    avifBool tileUVPresent = (firstTile->image->yuvPlanes[AVIF_CHAN_U] && firstTile->image->yuvPlanes[AVIF_CHAN_V]);
 
     for (unsigned int i = 1; i < tileCount; ++i) {
         avifTile * tile = &data->tiles.tile[firstTileIndex + i];
@@ -678,11 +677,7 @@
 
 static avifBool isAlphaURN(char * urn)
 {
-    if (!strcmp(urn, URN_ALPHA0))
-        return AVIF_TRUE;
-    if (!strcmp(urn, URN_ALPHA1))
-        return AVIF_TRUE;
-    return AVIF_FALSE;
+    return !strcmp(urn, URN_ALPHA0) || !strcmp(urn, URN_ALPHA1);
 }
 
 // ---------------------------------------------------------------------------