Remove Cppcheck from the distribution

I was initially impressed with its output, but over time I've found it
less and less useful. I hardly use it anymore, and it would at best be
neglected if left in the distribution. The build script is retained in
the contrib/ directory, and it's easy to build natively from source.

contrib/cppcheck.mak

@@ -0,0 +1,8 @@
+ext      := $(shell find externals -mindepth 1 -type d)
+src      := $(shell find cli lib externals -name '*.cpp')
+obj      := $(src:.cpp=.o)
+CXXFLAGS := -w -Os -Ilib $(addprefix -I,$(ext))
+cppcheck.exe: $(obj)
+	$(CXX) -s -o $@ $(obj) -lshlwapi
+cppcheck: $(obj)
+	$(CXX) -pthread -s -o $@ $(obj)