Do not hardcode library version number.

Index: Makefile.in
--- Makefile.in.orig
+++ Makefile.in
@@ -858,7 +858,7 @@ src_libadplug_la_SOURCES = \
 	src/xad.cpp \
 	src/xsm.cpp
 
-src_libadplug_la_LDFLAGS = -release $(PACKAGE_VERSION) -version-info 0
+src_libadplug_la_LDFLAGS = -version-info 0
 src_libadplug_la_LIBADD = $(libbinio_LIBS)
 
 # -Dstricmp=strcasecmp is a hack. Throughout AdPlug, stricmp() is used to do