asahi: Remove unused #define

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24258>

src/asahi/lib/agx_nir_lower_alpha.c

@@ -7,8 +7,6 @@
 #include "agx_tilebuffer.h"
 #include "nir_builder.h"
 
-#define ALL_SAMPLES (0xFF)
-
 /*
  * Lower alpha-to-coverage to sample_mask and some math. May run on either a
  * monolithic pixel shader or a fragment epilogue.

src/asahi/lib/agx_nir_lower_msaa.c

@@ -8,8 +8,6 @@
 #include "nir.h"
 #include "nir_builder.h"
 
-#define ALL_SAMPLES (0xFF)
-
 static bool
 lower_wrapped(nir_builder *b, nir_instr *instr, void *data)
 {