avcodec/texturedspenc: Remove unused rgtc1_u_alpha encoding func

Effectively reverts 50a20de6b9.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavcodec/texturedspenc.c

@@ -647,28 +647,11 @@ static int dxt5ys_block(uint8_t *dst, ptrdiff_t stride, const uint8_t *block)
     return 16;
 }
 
-/**
- * Compress one block of RGBA pixels in a RGTC1U texture and store the
- * resulting bytes in 'dst'. Use the alpha channel of the input image.
- *
- * @param dst    output buffer.
- * @param stride scanline in bytes.
- * @param block  block to compress.
- * @return how much texture data has been written.
- */
-static int rgtc1u_alpha_block(uint8_t *dst, ptrdiff_t stride, const uint8_t *block)
-{
-    compress_alpha(dst, stride, block);
-
-    return 8;
-}
-
 av_cold void ff_texturedspenc_init(TextureDSPContext *c)
 {
     c->dxt1_block         = dxt1_block;
     c->dxt5_block         = dxt5_block;
     c->dxt5ys_block       = dxt5ys_block;
-    c->rgtc1u_alpha_block = rgtc1u_alpha_block;
 }
 
 #define TEXTUREDSP_FUNC_NAME ff_texturedsp_compress_thread