libwebp: remove unneeded defines

Signed-off-by: James Almer <jamrial@gmail.com>

configure

@@ -1695,7 +1695,6 @@ HEADERS_LIST="
     udplite_h
     unistd_h
     valgrind_valgrind_h
-    webp_mux_h
     windows_h
     winsock2_h
 "
@@ -1898,7 +1897,6 @@ CONFIG_EXTRA="
     intrax8
     jpegtables
     lgplv3
-    libwebp_anim
     llauddsp
     llviddsp
     lpc

libavcodec/libwebpenc_animencoder.c

@@ -27,9 +27,7 @@
 #include "config.h"
 #include "libwebpenc_common.h"
 
-#if HAVE_WEBP_MUX_H
 #include <webp/mux.h>
-#endif
 
 typedef struct LibWebPAnimContext {
     LibWebPContextCommon cc;