remove pointless discards in test cases

test/cases/compile_errors/non-comptime-parameter-used-as-array-size.zig

@@ -6,7 +6,6 @@ export fn entry() void {
 }
 
 fn makeLlamas(count: usize) [count]u8 {
-    _ = count;
 }
 
 // error

test/cases/type_of.0.zig

@@ -1,6 +1,5 @@
 pub fn main() void {
     var x: usize = 0;
-    _ = x;
     const z = @TypeOf(x, @as(u128, 5));
     assert(z == u128);
 }