Use ESSL 1.0 for EGLRenderer shaders

We still ostensibly support GLES 2.0 GPUs.

app/shaders/egl_opaque.frag

@@ -1,12 +1,10 @@
-#version 300 es
 #extension GL_OES_EGL_image_external : require
 precision mediump float;
-out vec4 FragColor;
 
-in vec2 vTextCoord;
+varying vec2 vTexCoord;
 
 uniform samplerExternalOES uTexture;
 
 void main() {
-        FragColor = texture2D(uTexture, vTextCoord);
+    gl_FragColor = texture2D(uTexture, vTexCoord);
 }