[codex] Let generic test turns inherit their environment (#27972)

## Why

The paired thread-environment migration changed several generic test
turn helpers from supplying a fallback cwd to explicitly selecting the
local environment. That changes their meaning under
`build_with_remote_env()`: remote-only fixtures cannot resolve the
forced local selection, so the tests fail before exercising apply-patch,
RMCP, unified-exec, or view-image behavior.

Generic helpers should inherit the environment selected by their
fixture. Tests that intentionally exercise local routing continue to
select the local environment explicitly.

## What changed

- Remove forced `local_selections(...)` overrides from the generic
apply-patch, RMCP, unified-exec, and view-image turn helpers.
- Remove the imports made unused by those deletions.

## Testing

- Not run locally; this is a test-fixture-only change and the `full-ci`
branch will exercise the affected remote shards.

codex-rs/core/tests/suite/apply_patch_cli.rs

@@ -7,7 +7,6 @@ use core_test_support::responses::ev_apply_patch_custom_tool_call;
 use core_test_support::responses::ev_apply_patch_shell_command_call_via_heredoc;
 use core_test_support::responses::ev_shell_command_call;
 use core_test_support::test_codex::ApplyPatchModelOutput;
-use core_test_support::test_codex::local_selections;
 use pretty_assertions::assert_eq;
 use std::fs;
 use std::path::PathBuf;
@@ -107,7 +106,6 @@ async fn submit_without_wait_with_turn_permissions(
             responsesapi_client_metadata: None,
             additional_context: Default::default(),
             thread_settings: codex_protocol::protocol::ThreadSettingsOverrides {
-                environments: Some(local_selections(harness.cwd_abs())),
                 approval_policy: Some(AskForApproval::Never),
                 sandbox_policy: Some(sandbox_policy),
                 permission_profile,

codex-rs/core/tests/suite/rmcp_client.rs

@@ -4,7 +4,6 @@ use anyhow::Context as _;
 use anyhow::ensure;
 use base64::Engine;
 use base64::engine::general_purpose::STANDARD as BASE64_STANDARD;
-use core_test_support::test_codex::local_selections;
 use std::collections::HashMap;
 use std::ffi::OsStr;
 use std::ffi::OsString;
@@ -142,7 +141,6 @@ fn user_turn_with_permission_profile(
         responsesapi_client_metadata: None,
         additional_context: Default::default(),
         thread_settings: codex_protocol::protocol::ThreadSettingsOverrides {
-            environments: Some(local_selections(cwd)),
             approval_policy: Some(AskForApproval::Never),
             sandbox_policy: Some(sandbox_policy),
             permission_profile,

codex-rs/core/tests/suite/unified_exec.rs

@@ -204,7 +204,6 @@ async fn submit_unified_exec_turn(
             responsesapi_client_metadata: None,
             additional_context: Default::default(),
             thread_settings: codex_protocol::protocol::ThreadSettingsOverrides {
-                environments: Some(local_selections(test.config.cwd.clone())),
                 approval_policy: Some(AskForApproval::Never),
                 sandbox_policy: Some(sandbox_policy),
                 permission_profile,

codex-rs/core/tests/suite/view_image.rs

@@ -45,7 +45,6 @@ use core_test_support::responses::start_mock_server;
 use core_test_support::skip_if_no_network;
 use core_test_support::test_codex::TestCodex;
 use core_test_support::test_codex::local;
-use core_test_support::test_codex::local_selections;
 use core_test_support::test_codex::test_codex;
 use core_test_support::test_codex::turn_permission_fields;
 use core_test_support::wait_for_event_with_timeout;
@@ -82,7 +81,6 @@ fn disabled_user_turn(test: &TestCodex, items: Vec<UserInput>, model: String) ->
         responsesapi_client_metadata: None,
         additional_context: Default::default(),
         thread_settings: codex_protocol::protocol::ThreadSettingsOverrides {
-            environments: Some(local_selections(test.config.cwd.clone())),
             approval_policy: Some(AskForApproval::Never),
             sandbox_policy: Some(sandbox_policy),
             permission_profile,