[Pal/{Linux, Linux-SGX}] Delete unused macro SEEK_SET

Pal/src/host/Linux-SGX/db_streams.c

@@ -161,10 +161,6 @@ int handle_serialize(PAL_HANDLE handle, void** data) {
     return hdlsz + dsz1 + dsz2;
 }
 
-#ifndef SEEK_SET
-#define SEEK_SET 0
-#endif
-
 int handle_deserialize(PAL_HANDLE* handle, const void* data, int size) {
     PAL_HANDLE hdl_data = (void*)data, hdl = NULL;
     int hdlsz = handle_size(hdl_data), ret = -PAL_ERROR_NOMEM;

Pal/src/host/Linux/db_files.c

@@ -66,10 +66,6 @@ static int file_open (PAL_HANDLE * handle, const char * type, const char * uri,
     return 0;
 }
 
-#ifndef SEEK_SET
-# define SEEK_SET 0
-#endif
-
 /* 'read' operation for file streams. */
 static int64_t file_read (PAL_HANDLE handle, uint64_t offset, uint64_t count,
                           void * buffer)

Pal/src/host/Linux/db_process.c

@@ -44,10 +44,6 @@ typedef __kernel_pid_t pid_t;
 #include <linux/types.h>
 #include <sys/socket.h>
 
-#ifndef SEEK_SET
-# define SEEK_SET 0
-#endif
-
 static inline int create_process_handle (PAL_HANDLE * parent,
                                          PAL_HANDLE * child)
 {

Pal/src/host/Linux/db_streams.c

@@ -168,10 +168,6 @@ int handle_serialize(PAL_HANDLE handle, void** data) {
     return hdlsz + dsz1 + dsz2;
 }
 
-#ifndef SEEK_SET
-#define SEEK_SET 0
-#endif
-
 int handle_deserialize(PAL_HANDLE* handle, const void* data, int size) {
     PAL_HANDLE hdl_data = (void*)data, hdl = NULL;
     int hdlsz = handle_size(hdl_data), ret = -PAL_ERROR_NOMEM;