config: remove unused shadow_color variable

Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>

src/config.c

@@ -515,7 +515,6 @@ char *parse_config(options_t *opt, const char *config_file, bool *shadow_enable,
 	    .sw_opti = false,
 	    .use_damage = true,
 
-	    .shadow_color = "#000000",
 	    .shadow_red = 0.0,
 	    .shadow_green = 0.0,
 	    .shadow_blue = 0.0,

src/config.h

@@ -140,7 +140,6 @@ typedef struct options {
 	// === Shadow ===
 	/// Red, green and blue tone of the shadow.
 	double shadow_red, shadow_green, shadow_blue;
-	char *shadow_color;
 	int shadow_radius;
 	int shadow_offset_x, shadow_offset_y;
 	double shadow_opacity;