Remove hir::Expr::MacroStmts

This hir expression isn't needed and only existed as it was simpler to
deal with at first as it gave us a direct mapping for the ast version of
the same construct. This PR removes it, properly handling the statements
that are introduced by macro call expressions.

crates/hir-expand/src/lib.rs

@@ -969,7 +969,7 @@ impl ExpandTo {
         if parent.kind() == MACRO_EXPR
             && parent
                 .parent()
-                .map_or(true, |p| matches!(p.kind(), EXPR_STMT | STMT_LIST | MACRO_STMTS))
+                .map_or(false, |p| matches!(p.kind(), EXPR_STMT | STMT_LIST | MACRO_STMTS))
         {
             return ExpandTo::Statements;
         }