common.h: general clean up

Remove unused functions and definitions. Move some macros into the files
they belong.

Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>

src/render.c

@@ -15,6 +15,11 @@
 #ifdef CONFIG_OPENGL
 #include "backend/gl/glx.h"
 #include "opengl.h"
+
+#ifndef GLX_BACK_BUFFER_AGE_EXT
+#define GLX_BACK_BUFFER_AGE_EXT 0x20F4
+#endif
+
 #endif
 
 #include "compiler.h"
@@ -31,6 +36,10 @@
 #include "backend/backend_common.h"
 #include "render.h"
 
+#define XRFILTER_CONVOLUTION "convolution"
+#define XRFILTER_GAUSSIAN "gaussian"
+#define XRFILTER_BINOMIAL "binomial"
+
 /**
  * Bind texture in paint_t if we are using GLX backend.
  */