checker: remove "use `++` instead of `+= 1`"

vlib/v/checker/checker.v

@@ -2871,15 +2871,6 @@ pub fn (mut c Checker) assign_stmt(mut assign_stmt ast.AssignStmt) {
 					&& left_sym.kind !in [.byteptr, .charptr, .struct_, .alias] {
 					c.error('invalid right operand: $left_sym.name $assign_stmt.op $right_sym.name',
 						right.position())
-				} else if right is ast.IntegerLiteral {
-					if right.val == '1' {
-						op := if assign_stmt.op == .plus_assign {
-							token.Kind.inc
-						} else {
-							token.Kind.dec
-						}
-						c.error('use `$op` instead of `$assign_stmt.op 1`', assign_stmt.pos)
-					}
 				}
 			}
 			.mult_assign, .div_assign {

vlib/v/checker/tests/plus_or_minus_assign_one_err.out

@@ -1,13 +0,0 @@
-vlib/v/checker/tests/plus_or_minus_assign_one_err.vv:3:6: error: use `++` instead of `+= 1`
-    1 | fn main() {
-    2 |     mut foo := 10
-    3 |     foo += 1
-      |         ~~
-    4 |     foo -= 1
-    5 | }
-vlib/v/checker/tests/plus_or_minus_assign_one_err.vv:4:6: error: use `--` instead of `-= 1`
-    2 |     mut foo := 10
-    3 |     foo += 1
-    4 |     foo -= 1
-      |         ~~
-    5 | }

vlib/v/checker/tests/plus_or_minus_assign_one_err.vv

@@ -1,5 +0,0 @@
-fn main() {
-	mut foo := 10
-	foo += 1
-	foo -= 1
-}