hash: move dummy map initialisation into an fn init(){}, so users do not have to do it explicitly to be compatible with -skip-unused

cmd/tools/bench/wyhash.v

@@ -6,9 +6,6 @@ import rand
 import benchmark
 
 fn main() {
-	_ := map{
-		1: 1
-	}
 	rand.seed([u32(42), 0])
 	sample_size := 10000000
 	min_str_len := 20

cmd/tools/vwipe-cache.v

@@ -4,9 +4,6 @@ import os
 import v.vcache
 
 fn main() {
-	_ := map{
-		1: 1
-	}
 	mut cm := vcache.new_cache_manager([])
 	cpath := cm.basepath
 	if os.exists(cpath) && os.is_dir(cpath) {