shader: replace texture2d with texture (#10893)

* shader: replace texture2d with texture

remove unused v_color and replace deprecated texture2d with texture.

* shader: use the more modern essl3 extension

GL_OES_EGL_image_external_essl3 provides support for samplerExternalOES
in texture function, aquamarine already use it. apply it here too.

src/render/shaders/glsl/rgbx.frag

@@ -20,7 +20,7 @@ void main() {
     if (discardOpaque == 1 && alpha == 1.0)
 	discard;
 
-    vec4 pixColor = vec4(texture2D(tex, v_texcoord).rgb, 1.0);
+    vec4 pixColor = vec4(texture(tex, v_texcoord).rgb, 1.0);
 
     if (applyTint == 1) {
 	    pixColor[0] = pixColor[0] * tint[0];