Remove duplicated assignment of compilation flags

Fixes a double "-g -O2 -g -O2" in compiler invocation.

c++/Makefile.am

@@ -4,7 +4,6 @@ lib_LTLIBRARIES = libhamlib++.la
 libhamlib___la_SOURCES = rigclass.cc rotclass.cc ampclass.cc
 libhamlib___la_LDFLAGS = -no-undefined -version-info $(ABI_VERSION):$(ABI_REVISION):$(ABI_AGE) $(LDFLAGS)
 libhamlib___la_LIBADD = $(top_builddir)/src/libhamlib.la
-AM_CXXFLAGS=$(CXXFLAGS)
 
 check_PROGRAMS = testcpp