tests: add .vv support for v vet too, and simplify vet_test.v

vlib/v/vet/tests/array_init_one_val.out

@@ -1,2 +1,2 @@
-vlib/v/vet/tests/array_init_one_val.v:2: Use `var == value` instead of `var in [value]`
+vlib/v/vet/tests/array_init_one_val.vv:2: Use `var == value` instead of `var in [value]`
 NB: You can run `v fmt -w file.v` to fix these automatically

vlib/v/vet/tests/indent_with_space.out

@@ -1,2 +1,2 @@
-vlib/v/vet/tests/indent_with_space.v:2: Looks like you are using spaces for indentation.
+vlib/v/vet/tests/indent_with_space.vv:2: Looks like you are using spaces for indentation.
 NB: You can run `v fmt -w file.v` to fix these automatically

vlib/v/vet/tests/parens_space_a.out

@@ -1,2 +1,2 @@
-vlib/v/vet/tests/parens_space_a.v:1: Looks like you are adding a space after `(`
+vlib/v/vet/tests/parens_space_a.vv:1: Looks like you are adding a space after `(`
 NB: You can run `v fmt -w file.v` to fix these automatically

vlib/v/vet/tests/parens_space_b.out

@@ -1,2 +1,2 @@
-vlib/v/vet/tests/parens_space_b.v:1: Looks like you are adding a space before `)`
+vlib/v/vet/tests/parens_space_b.vv:1: Looks like you are adding a space before `)`
 NB: You can run `v fmt -w file.v` to fix these automatically

vlib/v/vet/vet_test.v

@@ -27,15 +27,12 @@ fn check_path(vexe, dir string, tests []string) int {
 		basepath: dir
 	})
 	for path in paths {
-		program := path.replace('.vv', '.v')
+		program := path
 		print(path + ' ')
-		os.cp(path, program) or {
-			panic(err)
-		}
 		res := os.exec('$vexe vet $program') or {
 			panic(err)
 		}
-		mut expected := os.read_file(program.replace('.v', '') + '.out') or {
+		mut expected := os.read_file(program.replace('.vv', '') + '.out') or {
 			panic(err)
 		}
 		expected = clean_line_endings(expected)
@@ -52,7 +49,6 @@ fn check_path(vexe, dir string, tests []string) int {
 			nb_fail++
 		} else {
 			println(term.green('OK'))
-			os.rm(program)
 		}
 	}
 	return nb_fail