libutil: remove unused FdSource::specialEndOfFileError

Change-Id: Ia03e270c359014ab3675a043bad342c4bbfdbafd

lix/libutil/serialise.cc

@@ -197,17 +197,11 @@ size_t FdSource::readUnbuffered(char * data, size_t len)
         throw SysError("reading from file");
     }
     if (n == 0) {
-        throw EndOfFile(endOfFileError());
+        throw EndOfFile("unexpected end-of-file");
     }
     return n;
 }
 
-std::string FdSource::endOfFileError() const
-{
-    return specialEndOfFileError.has_value() ? *specialEndOfFileError : "unexpected end-of-file";
-}
-
-
 size_t StringSource::read(char * data, size_t len)
 {
     if (pos == s.size()) throw EndOfFile("end of string reached");

lix/libutil/serialise.hh

@@ -152,10 +152,6 @@ private:
 struct FdSource : BufferedSource
 {
     int fd;
-    /** Defaults to "unexpected end-of-file" */
-    std::optional<std::string> specialEndOfFileError;
-
-    std::string endOfFileError() const;
 
     FdSource() : fd(-1) { }
     FdSource(int fd) : fd(fd) { }