build: Drop explicit check for dlfcn.h

It is detected as a part of the libdl check.

configure

@@ -1568,7 +1568,6 @@ HEADERS_LIST="
     dev_video_bktr_ioctl_bt848_h
     dev_video_meteor_ioctl_meteor_h
     direct_h
-    dlfcn_h
     dxgidebug_h
     dxva_h
     gsm_h
@@ -4658,7 +4657,6 @@ check_struct windows.h "CONDITION_VARIABLE" Ptr
 
 check_header d3d11.h
 check_header direct.h
-check_header dlfcn.h
 check_header dxgidebug.h
 check_header dxva.h
 check_header dxva2api.h

libavcodec/nvenc.c

@@ -28,12 +28,7 @@
 
 #define CUDA_LIBNAME "libcuda.so"
 
-#if HAVE_DLFCN_H
-#include <dlfcn.h>
-
-#define NVENC_LIBNAME "libnvidia-encode.so"
-
-#elif HAVE_WINDOWS_H
+#if HAVE_WINDOWS_H
 #include <windows.h>
 
 #if ARCH_X86_64
@@ -45,6 +40,9 @@
 #define dlopen(filename, flags) LoadLibrary((filename))
 #define dlsym(handle, symbol)   GetProcAddress(handle, symbol)
 #define dlclose(handle)         FreeLibrary(handle)
+#else
+#include <dlfcn.h>
+#define NVENC_LIBNAME "libnvidia-encode.so"
 #endif
 
 #include "libavutil/common.h"