Remove plugins dependency on libvlccore.sym

In practice, this is useless.

modules/genmf

@@ -60,7 +60,7 @@ lib${mod}_plugin_la_CXXFLAGS = \$(AM_CXXFLAGS)
 lib${mod}_plugin_la_OBJCFLAGS = \$(AM_OBJCFLAGS)
 # Set LIBADD and DEPENDENCIES manually:
 lib${mod}_plugin_la_LIBADD = \$(AM_LIBADD)
-lib${mod}_plugin_la_DEPENDENCIES = \$(top_srcdir)/src/libvlccore.sym
+lib${mod}_plugin_la_DEPENDENCIES =
 
 EOF
   done