Simplify autodependency examples.

Turns out we don't need sed to process the output of gcc -MD.  We can just
do this:

	read DEPS <filename.deps

The 'read' command in sh actually handles backslashes correctly, so we don't
have to sed them out after all.  And then a simple ${DEPS#*:} removes the
"target:" prefix from the dependency line, and we're done!

t/example/CC.do

@@ -3,9 +3,9 @@ redo-ifchange config.sh
 exec >$3
 cat <<-EOF
 	redo-ifchange \$1.c
-	gcc $CFLAGS -MD -MF \$3.deps.tmp -o \$3 -c \$1.c
-	DEPS=\$(sed -e "s/^\$3://" -e 's/\\\\//g' <\$3.deps.tmp)
-	rm -f \$3.deps.tmp
-	redo-ifchange \$DEPS
+	gcc $CFLAGS -MD -MF \$3.deps -o \$3 -c \$1.c
+	read DEPS <\$3.deps
+	rm -f \$3.deps
+	redo-ifchange \${DEPS#*:}
 EOF
 chmod +x $3