Omit check_sorted dependencies no longer needed

* Makefile (check_sorted): Omit unnecessary dependencies on
iso3166.tab, zone.tab, zone1970.tab.  They should have been
removed in commit 1bb4263bb1716fe3ba63b26600adc9c32f1fe16e dated
2019-06-22 13:55:46 -0700.

Makefile

@@ -837,7 +837,7 @@ check_slashed_abbrs: $(TDATA_TO_CHECK)
 
 CHECK_CC_LIST = { n = split($$1,a,/,/); for (i=2; i<=n; i++) print a[1], a[i]; }
 
-check_sorted: backward backzone iso3166.tab zone.tab zone1970.tab
+check_sorted: backward backzone
 		$(AWK) '/^Link/ {printf "%.5d %s\n", g, $$3} !/./ {g++}' \
 		  backward | LC_ALL=C sort -cu
 		$(AWK) '/^Zone/ {print $$2}' backzone | LC_ALL=C sort -cu