refactor(config)!: remove deprecated .proselintrc (amperser#1471)

- Remove deprecation warning and read system for old configuration files
- Remove references to legacy configuration in `README`

BREAKING CHANGE:

Bare .proselintrc files are no longer read. Relocate your configuration accordingly.

Author: Nytelife26

README.md

@@ -200,10 +200,7 @@ This will return a list of suggestions:
 
 You can disable any of the checks by modifying
 `$XDG_CONFIG_HOME/proselint/config.json`. If `$XDG_CONFIG_HOME` is not set or
-empty, `~/.config/proselint/config.json` will be used. Additionally, for
-compatibility reasons, the legacy configurations `~/.proselintrc` and
-`$XDG_CONFIG_HOME/proselint/config` will be checked if
-`$XDG_CONFIG_HOME/proselint/config.json` does not exist. Check selection is
+empty, `~/.config/proselint/config.json` will be used. Check selection is
 granular at any level, illustrated in the following example:
 
 ```json

proselint/config/__init__.py

@@ -6,7 +6,6 @@
 from itertools import chain
 from pathlib import Path
 from typing import TypeAlias, TypedDict, TypeVar, cast
-from warnings import showwarning as warn
 
 from proselint import config
 from proselint.config import paths
@@ -81,19 +80,11 @@ def load_from(config_path: Path | None = None) -> Config:
     result = DEFAULT
     config_paths = paths.config_paths + ([config_path] if config_path else [])
 
-    for path in config_paths:
-        if path.is_file():
-            result = _deepmerge_dicts(
-                cast("dict[str, object]", result),
-                json.loads(path.read_text()),  # pyright: ignore[reportAny]
-            )
-        if path.suffix == ".json" and (old := path.with_suffix("")).is_file():
-            warn(
-                f"{old} was found instead of a JSON file. Rename to {path}.",
-                DeprecationWarning,
-                "",
-                0,
-            )
+    for path in filter(Path.is_file, config_paths):
+        result = _deepmerge_dicts(
+            cast("dict[str, object]", result),
+            json.loads(path.read_text()),  # pyright: ignore[reportAny]
+        )
 
     result = cast("Config", result)