Remove useless DEFAULT_INCLUDES in AM_CCASFLAGS

CPPASCOMPILE and LTCPPASCOMPILE all include DEFAULT_INCLUDES,
hence it's unnecessary to add the includes again.

Signed-off-by: Pengcheng Xu <i@jsteward.moe>

lib/libspl/Makefile.am

@@ -13,7 +13,6 @@ DEFAULT_INCLUDES += \
 	-I$(top_srcdir)/lib/libspl/include
 
 AM_CCASFLAGS = \
-	-I$(top_srcdir)/lib/libspl/include \
 	$(CFLAGS)
 
 noinst_LTLIBRARIES = libspl.la