mesa: remove the MESA_NO_DITHER env var

This was sometimes useful back when 16-bit framebuffers were prominent.

src/mesa/main/debug.c

@@ -213,16 +213,6 @@ void
 _mesa_init_debug( struct gl_context *ctx )
 {
    char *c;
-
-   /* Dither disable */
-   ctx->NoDither = _mesa_getenv("MESA_NO_DITHER") ? GL_TRUE : GL_FALSE;
-   if (ctx->NoDither) {
-      if (_mesa_getenv("MESA_DEBUG")) {
-         _mesa_debug(ctx, "MESA_NO_DITHER set - dithering disabled\n");
-      }
-      ctx->Color.DitherFlag = GL_FALSE;
-   }
-
    c = _mesa_getenv("MESA_DEBUG");
    if (c)
       add_debug_flags(c);

src/mesa/main/enable.c

@@ -352,9 +352,6 @@ _mesa_set_enable(struct gl_context *ctx, GLenum cap, GLboolean state)
          ctx->Depth.Test = state;
          break;
       case GL_DITHER:
-         if (ctx->NoDither) {
-            state = GL_FALSE; /* MESA_NO_DITHER env var */
-         }
          if (ctx->Color.DitherFlag == state)
             return;
          FLUSH_VERTICES(ctx, _NEW_COLOR);

src/mesa/main/mtypes.h

@@ -3295,9 +3295,6 @@ struct gl_context
    GLboolean FirstTimeCurrent;
    /*@}*/
 
-   /** Dither disable via MESA_NO_DITHER env var */
-   GLboolean NoDither;
-
    /** software compression/decompression supported or not */
    GLboolean Mesa_DXTn;