gl renderer: Remove some unused uniforms

gsk/gl/gskglrenderopsprivate.h

@@ -44,7 +44,6 @@ struct _Program
   int position_location;
   int uv_location;
   int alpha_location;
-  int blend_mode_location;
   int viewport_location;
   int projection_location;
   int modelview_location;

gsk/resources/glsl/es2_common.fs.glsl

@@ -1,11 +1,9 @@
 precision mediump float;
 
 uniform sampler2D u_source;
-uniform sampler2D u_mask;
 uniform mat4 u_projection;
 uniform mat4 u_modelview;
 uniform float u_alpha;
-uniform int uBlendMode;
 uniform vec4 u_viewport;
 
 // In GtkSnapshot coordinates

gsk/resources/glsl/gl3_common.fs.glsl

@@ -1,11 +1,9 @@
 precision highp float;
 
 uniform sampler2D u_source;
-uniform sampler2D u_mask;
 uniform mat4 u_projection = mat4(1.0);
 uniform mat4 u_modelview = mat4(1.0);
 uniform float u_alpha = 1.0;
-uniform int uBlendMode;
 uniform vec4 u_viewport;
 
 // In GtkSnapshot coordinates

gsk/resources/glsl/gl_common.fs.glsl

@@ -1,9 +1,7 @@
 uniform sampler2D u_source;
-uniform sampler2D u_mask;
 uniform mat4 u_projection;
 uniform mat4 u_modelview;
 uniform float u_alpha;
-uniform int uBlendMode;
 uniform vec4 u_viewport;
 
 // In GtkSnapshot coordinates