Remove unneeded 'once' guards

This is guarateed by pthread_once now

src/qm.c

@@ -3105,9 +3105,7 @@ static void untriangle(uint8_t *dst, const uint8_t *src, const int sz) {
 }
 
 void av1_init_qm_tables(void) {
-    static int done = 0;
-    if (done) return;
-    done = 1;
+    // This function is guaranteed to be called only once by dav1d_init
 
     for (int i = 0; i < 15; i++)
         for (int j = 0; j < 2; j++) {

src/wedge.c

@@ -214,9 +214,7 @@ static void fill2d_16x2(uint8_t *dst, const int w, const int h,
 }
 
 void av1_init_wedge_masks(void) {
-    static int done = 0;
-    if (done) return;
-    done = 1;
+    // This function is guaranteed to be called only once by dav1d_init
 
     enum WedgeMasterLineType {
         WEDGE_MASTER_LINE_ODD,
@@ -315,9 +313,7 @@ static void build_nondc_ii_masks(uint8_t *const mask_v,
 }
 
 void av1_init_interintra_masks(void) {
-    static int done = 0;
-    if (done) return;
-    done = 1;
+    // This function is guaranteed to be called only once by dav1d_init
 
     memset(ii_dc_mask, 32, 32 * 32);
 #define set(a) a[II_VERT_PRED - 1], a[II_HOR_PRED - 1], a[II_SMOOTH_PRED - 1]