refactor(plan): Phase 273 P3+ - Legacy code removal

Phase 273 P3+ 完成: レガシーコード削除 + 未使用 import 整理

Removed Legacy Items:
1. emit_scan_with_init_edgecfg() - Pattern6 固有の emission 関数
   - File deleted: src/mir/builder/emission/loop_scan_with_init.rs (~144 lines)
   - Replaced by: generalized Frag API (Phase 273 P2)

2. CoreCarrierInfo struct - Legacy carrier representation
   - Removed from: src/mir/builder/control_flow/plan/mod.rs (~15 lines)
   - Replaced by: CorePhiInfo (generalized PHI representation)

3. verify_carrier() function - CoreCarrierInfo validator
   - Removed from: src/mir/builder/control_flow/plan/verifier.rs (~15 lines)
   - Replaced by: generalized PHI verification (V7-V9)

Code Cleanup:
- cargo fix applied: unused imports removed (~30 files)
- Verifier invariants updated: V1→V2-V9 (carrier→PHI model)
- Module declaration cleanup in emission/mod.rs

Impact:
- Total lines removed: ~174 lines (net reduction)
- Pattern-agnostic architecture strengthened
- All legacy Pattern6 references eliminated

Tests:
- ✅ VM tests PASS (phase254/256/258)
- ✅ LLVM tests PASS (phase256/258)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/mir/join_ir_vm_bridge/handlers/jump.rs

@@ -89,10 +89,9 @@
 //!   jump_args_layout = CarriersOnly
 //! ```
 
-use crate::ast::Span;
 use crate::mir::join_ir::{JoinContId, JoinFuncId};
 use crate::mir::join_ir::lowering::inline_boundary::JumpArgsLayout;
-use crate::mir::{BasicBlock, BasicBlockId, EffectMask, MirFunction, MirInstruction, ValueId};
+use crate::mir::{BasicBlock, BasicBlockId, MirFunction, MirInstruction, ValueId};
 use std::collections::BTreeMap;
 
 use super::super::{join_func_name, JoinIrVmBridgeError};

src/mir/join_ir_vm_bridge/joinir_function_converter.rs

@@ -6,9 +6,7 @@
 //! - 関数署名の管理
 
 use crate::mir::join_ir::{JoinFuncId, JoinFunction, JoinModule};
-use crate::mir::phi_core::copy_type_propagator::CopyTypePropagator;
-use crate::mir::phi_core::phi_type_resolver::PhiTypeResolver;
-use crate::mir::{BasicBlockId, EffectMask, FunctionSignature, MirFunction, MirInstruction, MirModule, MirType};
+use crate::mir::{BasicBlockId, EffectMask, FunctionSignature, MirFunction, MirModule, MirType};
 use std::collections::BTreeMap;
 
 use super::join_func_name;