*: kill bb_get_last_path_component, replace with two functions

(one which strips trailing slash and one which does not)
wget: straighten out as a result of above change
   text    data     bss     dec     hex filename
   5056       1       0    5057    13c1 busybox.t4/networking/wget.o
   5022       0       0    5022    139e busybox.t5/networking/wget.o

coreutils/cp.c

@@ -87,7 +87,7 @@ int cp_main(int argc, char **argv)
 	}
 
 	while (1) {
-		dest = concat_path_file(last, bb_get_last_path_component(*argv));
+		dest = concat_path_file(last, bb_get_last_path_component_strip(*argv));
  DO_COPY:
 		if (copy_file(*argv, dest, flags) < 0) {
 			status = 1;