Revert "CFG: revert change for single-stmt block"

This reverts commit 9f6af5a.

This is a revert of a revert of b406023

b406023 was causing some regression
test failures but that was because the patcher side of things had not
been merged.

Author: waskyo

chb/app/Cfg.py

@@ -477,8 +477,6 @@ def stmt_ast(
         fn = astfn.function
 
         def mk_block(stmts: List[AST.ASTStmt]) -> AST.ASTStmt:
-            if len(stmts) == 1 and not stmts[0].is_ast_instruction_sequence:
-                return stmts[0]
             return astree.mk_block(stmts)
 
         gotolabels: Set[str] = set() # this is both used and mutated by run_with_gotolabels()