OpenGL: also remove VAO from xfb convertion

We use attributeless rendering, so officially we have to bind _any_ VAO.
As the state of this VAO doesn't matter, we don't have to switch it.

Also fix an AMD issue as they don't like to render from an empty VAO.

Source/Core/VideoBackends/OGL/Src/TextureConverter.cpp

@@ -42,7 +42,6 @@ static SHADER s_encodingPrograms[NUM_ENCODING_PROGRAMS];
 
 static GLuint s_encode_VBO = 0;
 static GLuint s_encode_VAO = 0;
-static GLuint s_decode_VAO = 0;
 static TargetRectangle s_cached_sourceRc;
 
 static const char *VProgram =
@@ -177,9 +176,6 @@ void Init()
 	s_cached_sourceRc.left = -1;
 	s_cached_sourceRc.right = -1;
 
-	glGenVertexArrays(1, &s_decode_VAO );
-	glBindVertexArray( s_decode_VAO );
-
 	glActiveTexture(GL_TEXTURE0 + 9);
 	glGenTextures(1, &s_srcTexture);
 	glBindTexture(getFbType(), s_srcTexture);
@@ -200,7 +196,6 @@ void Shutdown()
 	glDeleteFramebuffers(1, &s_texConvFrameBuffer);
 	glDeleteBuffers(1, &s_encode_VBO );
 	glDeleteVertexArrays(1, &s_encode_VAO );
-	glDeleteVertexArrays(1, &s_decode_VAO );
 
 	s_rgbToYuyvProgram.Destroy();
 	s_yuyvToRgbProgram.Destroy();
@@ -405,7 +400,6 @@ void DecodeToTexture(u32 xfbAddr, int srcWidth, int srcHeight, GLuint destTextur
 	glViewport(0, 0, srcWidth, srcHeight);
 	s_yuyvToRgbProgram.Bind();
 
-	glBindVertexArray( s_decode_VAO );
 	glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
 
 	FramebufferManager::SetFramebuffer(0);