Makefile: remove obsolete variable

Makefile

@@ -2,9 +2,6 @@ BASENAME = demo
 
 BUILDDIR = build
 VARIANTS = presentation handout notes
-TARGETS  = $(BASENAME)-presentation.pdf \
-           $(BASENAME)-handout.pdf      \
-           $(BASENAME)-notes.pdf
 
 # Environment
 TEXDIRS = resources/latex/:resources/latex-sty/:resources/images/:resources/listings/
@@ -17,7 +14,7 @@ LATEXMK = export TYPE= TARGET="$(basename $(notdir $1))" && latexmk $(basename $
 VIEWER = xdg-open
 
 # main targets
-all: $(TARGETS)
+all: $(VARIANTS)
 
 clean:
 	find $(BUILDDIR) -type f -not -name "*.pdf" -delete