[client] egl: remove needless precision quantifiers

We simply use precision mediump float; for everything. We don't actually
need highp anyways, and we don't use it for stuff like CAS or FSR.

client/renderers/EGL/shader/splash_bg.frag

@@ -1,7 +1,8 @@
 #version 300 es
+precision mediump float;
 
-in  highp vec3  pos;
-out highp vec4  color;
+in  vec3  pos;
+out vec4  color;
 
 uniform sampler2D sampler1;