Remove support for DMA-BUF flags

They are never used in practice, which makes all of our flag
handling effectively dead code. Also, APIs such as KMS don't
provide a good way to deal with the flags. Let's just fail the
DMA-BUF import when clients provide flags.

include/wlr/render/dmabuf.h

@@ -14,16 +14,9 @@
 
 #define WLR_DMABUF_MAX_PLANES 4
 
-enum wlr_dmabuf_attributes_flags {
-	WLR_DMABUF_ATTRIBUTES_FLAGS_Y_INVERT = 1 << 0,
-	WLR_DMABUF_ATTRIBUTES_FLAGS_INTERLACED = 1 << 1,
-	WLR_DMABUF_ATTRIBUTES_FLAGS_BOTTOM_FIRST = 1 << 2,
-};
-
 struct wlr_dmabuf_attributes {
 	int32_t width, height;
 	uint32_t format;
-	uint32_t flags; // enum wlr_dmabuf_attributes_flags
 	uint64_t modifier;
 
 	int n_planes;

include/wlr/render/gles2.h

@@ -30,7 +30,6 @@ struct wlr_gles2_texture_attribs {
 	GLenum target; /* either GL_TEXTURE_2D or GL_TEXTURE_EXTERNAL_OES */
 	GLuint tex;
 
-	bool inverted_y;
 	bool has_alpha;
 };