This commit is the first in a series of similar commits to clean up
obsolete `extern crate` statements

Since Rust 1.30, normal macros can be imported via `use`, and with Rust
1.31 and edition 2018 this has become the preferred approach.
`extern crate` is only needed for `alloc` in `no_std` crates, which does
not apply here.

By dropping these (often redundant or odd) `extern crate` lines, we
expose the actual dependencies more clearly and reduce technical debt.

## Auto-generation of the series

Most of this series was produced automatically:

1. Removed all "extern crate" references
2. Run the script [0] to add missing `use` statements
3. Run `cargo +nightly fmt --all`
4. Fix the remaining problems manually

The treewide changes were then split into per-folder commits.

[0]
```python
import os
import re

# Mapping of macro/function usage to imports
MACRO_IMPORTS = {
    "info!": "use log::info;\n",
    "debug!": "use log::debug;\n",
    "error!": "use log::error;\n",
    "trace!": "use log::trace;\n",
    "warn!": "use log::warn;\n",
    "event!": "use event_monitor::event;\n",
    "anyhow!(": "use anyhow::anyhow;\n",
    "bitflags!(": "use bitflags::bitflags;\n",
    "ioctl_ior_nr!": "use vmm_sys_util::{ioctl_ior_nr};\n",
    "ioctl_iow_nr!": "use vmm_sys_util::{ioctl_iow_nr};\n",
}

# Regex for finding the first use statement
USE_REGEX = re.compile(r"^\s*(use|pub use) .+?;")

def process_file(path):
    with open(path, "r", encoding="utf-8") as f:
        lines = f.readlines()

    content = "".join(lines)
    existing_imports = set(lines)
    needed_imports = set()

    # Check macros/functions against mapping, only add if not already present
    for key, import_stmt in MACRO_IMPORTS.items():
        if key in content and import_stmt not in existing_imports:
            needed_imports.add(import_stmt)

    if not needed_imports:
        print(f"Unmodified {path} (no new imports needed)")
        return  # Nothing to do

    # Find first use or pub use statement
    for i, line in enumerate(lines):
        if USE_REGEX.match(line):
            insertion_index = i + 1
            break
    else:
        print(f"Unmodified {path} (no use or pub use statement found)")
        return  # No use statement found, skip file

    # Insert imports
    lines[insertion_index:insertion_index] = list(needed_imports)

    # Write back file
    with open(path, "w", encoding="utf-8") as f:
        f.writelines(lines)

    print(f"Modified {path}, added imports: {''.join(needed_imports).strip()}")

for root, _, files in os.walk("."):
    for file in files:
        if file.endswith(".rs"):
            process_file(os.path.join(root, file))
```

Signed-off-by: Philipp Schuster <[email protected]>
On-behalf-of: SAP [email protected]

This commit is part of a series of similar commits.

Signed-off-by: Philipp Schuster <[email protected]>
On-behalf-of: SAP [email protected]