remove lseek and size of fs stream

@@ -129,17 +129,6 @@ int SrsFileStream::write(void* buf, size_t count, ssize_t* pnwrite)
     return ret;
 }
 
-int64_t SrsFileStream::size()
-{
-    ::lseek(fd, 0, SEEK_SET);
-    return ::lseek(fd, 0, SEEK_END);
-}
-
-off_t SrsFileStream::lseek(off_t offset)
-{
-    return ::lseek(fd, offset, SEEK_SET);
-}
-
 SrsFlvEncoder::SrsFlvEncoder()
 {
     _fs = NULL;
@@ -164,9 +153,6 @@ int SrsFlvEncoder::write_header()
 {
     int ret = ERROR_SUCCESS;
     
-    // seek to header.
-    _fs->lseek(0);
-    
     static char flv_header[] = {
         'F', 'L', 'V', // Signatures "FLV"
         (char)0x01, // File version (for example, 0x01 for FLV version 1)

@@ -60,15 +60,6 @@ public:
     * @param pnwrite, return the write size. NULL to ignore.
     */
     virtual int write(void* buf, size_t count, ssize_t* pnwrite);
-public:
-    /**
-    * get size of file.
-    */
-    virtual int64_t size();
-    /**
-    * wrapper for system lseek where whence always use SEEK_SET
-    */
-    virtual off_t lseek(off_t offset);
 };
 
 /**