internal/sdref: Remove in favor of stdplus/handle

We no longer need to roll our own managed handle type now that stdplus
implements a generic one.

Tested:
    Built and run through unit tests.

Change-Id: Id34cd8d3ffacf7901d49cac335fa93f744f0e310
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/Makefile.am b/Makefile.am
index 8c7e40d..e27fbe8 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -38,11 +38,12 @@
 endif
 
 export AM_CPPFLAGS = -I$(abs_builddir)/src -I$(abs_srcdir)/src \
-                     $(SYSTEMD_CFLAGS) $(CODE_COVERAGE_CPPFLAGS)
+                     $(SYSTEMD_CFLAGS) $(STDPLUS_CFLAGS) \
+                     $(CODE_COVERAGE_CPPFLAGS)
 export AM_CFLAGS = $(CODE_COVERAGE_CFLAGS)
 export AM_CXXFLAGS = $(CODE_COVERAGE_CXXFLAGS)
 
-export COMMON_LIBS = $(SYSTEMD_LIBS) $(CODE_COVERAGE_LIBS)
+export COMMON_LIBS = $(SYSTEMD_LIBS) $(STDPLUS_LIBS) $(CODE_COVERAGE_LIBS)
 export SDEVENTPLUS_LIBS = $(abs_builddir)/src/libsdeventplus.la $(COMMON_LIBS)