Remove call_price field from get_call_orders()

**Bug Description**

`get_call_orders()` response contains `call_price` field which is always 1:1

```
[{'id': '1.8.88448',
'borrower': '1.2.415609',
'collateral': '86439389367',
'debt': 1306857052,
'call_price': {'base': {'amount': 1, 'asset_id': '1.3.0'},
'quote': {'amount': 1, 'asset_id': '1.3.113'}},
'target_collateral_ratio': 1610}]
```

**Impacts**
Describe which portion(s) of BitShares Core may be impacted by this bug. Please tick at least one box.
- [x] API (the application programming interface)
- [ ] Build (the build process or something prior to compiled code)
- [ ] CLI (the command line wallet)
- [ ] Deployment (the deployment process after building such as Docker, Travis, etc.)
- [ ] DEX (the Decentralized EXchange, market engine, etc.)
- [ ] P2P (the peer-to-peer network for transaction/block propagation)
- [ ] Performance (system or user efficiency, etc.)
- [ ] Protocol (the blockchain logic, consensus, validation, etc.)
- [ ] Security (the security of system or user data, etc.)
- [ ] UX (the User Experience)
- [ ] Other (please add below)

**Expected Behavior**

`call_price` field should be properly calculated or should not present at all (field removed from response).

## CORE TEAM TASK LIST
- [ ] Evaluate / Prioritize Bug Report
- [ ] Refine User Stories / Requirements
- [ ] Define Test Cases
- [ ] Design / Develop Solution
- [ ] Perform QA/Testing
- [ ] Update Documentation

Start by locating the C++ API entry point for get_call_orders() and trace how its response fields are assembled. The issue names no file or test and leaves two possible outcomes—calculating call_price or removing it—so clarify that decision before validating the response shape.

Written by the indexing model from the issue text.