all: use gometalinter.v2, fix new gosimple issues (#15650)

core/asm/asm.go

@@ -114,10 +114,7 @@ func PrintDisassembled(code string) error {
 			fmt.Printf("%06v: %v\n", it.PC(), it.Op())
 		}
 	}
-	if err := it.Error(); err != nil {
-		return err
-	}
-	return nil
+	return it.Error()
 }
 
 // Return all disassembled EVM instructions in human-readable format.

core/asm/compiler.go

@@ -237,10 +237,7 @@ func (c *Compiler) pushBin(v interface{}) {
 // isPush returns whether the string op is either any of
 // push(N).
 func isPush(op string) bool {
-	if op == "push" {
-		return true
-	}
-	return false
+	return op == "push"
 }
 
 // isJump returns whether the string op is jump(i)