Remove the drain argument from readFile

Now it is always `drain` (see previous commit).

src/libutil/serialise.hh

@@ -148,6 +148,9 @@ struct StringSink : Sink
 {
     ref<std::string> s;
     StringSink() : s(make_ref<std::string>()) { };
+    explicit StringSink(const size_t reservedSize) : s(make_ref<std::string>()) {
+      s->reserve(reservedSize);
+    };
     StringSink(ref<std::string> s) : s(s) { };
     void operator () (const unsigned char * data, size_t len) override;
 };

src/libutil/util.cc

@@ -316,12 +316,12 @@ string readFile(int fd)
 }
 
 
-string readFile(const Path & path, bool drain)
+string readFile(const Path & path)
 {
     AutoCloseFD fd = open(path.c_str(), O_RDONLY | O_CLOEXEC);
     if (!fd)
         throw SysError(format("opening file '%1%'") % path);
-    return drain ? drainFD(fd.get()) : readFile(fd.get());
+    return readFile(fd.get());
 }
 
 

src/libutil/util.hh

@@ -103,7 +103,7 @@ unsigned char getFileType(const Path & path);
 
 /* Read the contents of a file into a string. */
 string readFile(int fd);
-string readFile(const Path & path, bool drain = false);
+string readFile(const Path & path);
 void readFile(const Path & path, Sink & sink);
 
 /* Write a string to a file. */