[util] Remove line buffering

Something weird seems to be going on. Just kill it.

Fixes https://github.com/harfbuzz/harfbuzz/issues/888
diff --git a/configure.ac b/configure.ac
index 031be4a..2831e59 100644
--- a/configure.ac
+++ b/configure.ac
@@ -79,7 +79,7 @@
 
 # Functions, and headers
 
-AC_CHECK_FUNCS(atexit mprotect sysconf getpagesize mmap isatty newlocale strtod_l setlinebuf)
+AC_CHECK_FUNCS(atexit mprotect sysconf getpagesize mmap isatty newlocale strtod_l)
 
 save_libs="$LIBS"
 LIBS="$LIBS -lm"