Remove pattern rule

The built-in pattern rule for compiling a C++ source file already
considers CXXFLAGS, so this default behaviour is exactly what we want.
This Makefile really is now stripped to its bare form.

tpl/Makefile.simple

@@ -8,9 +8,6 @@ endif
 
 .PHONY: clean
 
-%.o: %.cpp
-	c++ $(CXXFLAGS) -c $<
-
 {PROJECT}: {PROJECT}.o
 	c++ -o {PROJECT} {PROJECT}.o