Revert "[LintDiff] Skip readme.md files with no "input-file:" string (Azure#35174)"

This reverts commit fc12f4e.

Author: mikeharder

eng/tools/lint-diff/src/processChanges.ts

@@ -135,18 +135,9 @@ export async function buildState(
   // For readme files that have changed but there are no affected swaggers,
   // add them to the map with no tags
   for (const changedReadme of existingChangedFiles.filter(readme)) {
-    const readmePath = resolve(rootPath, changedReadme);
-
-    // Skip readme.md files that don't have "input-file:" as autorest cannot
-    // scan them.
-    const readmeContent = await readFile(readmePath, { encoding: "utf-8" });
-    if (!readmeContent.includes("input-file:")) {
-      continue;
-    }
-
     const service = specModels.get(getService(changedReadme))!;
     const readmes = await service.getReadmes();
-    const readmeObject = readmes.get(readmePath)!;
+    const readmeObject = readmes.get(resolve(rootPath, changedReadme))!;
 
     if (!changedFileAndTagsMap.has(changedReadme)) {
       changedFileAndTagsMap.set(changedReadme, {

eng/tools/lint-diff/test/fixtures/buildState/specification/no-input-file/readme.md

@@ -249,13 +249,4 @@ describe("buildState", () => {
       ),
     ).not.toThrow();
   });
-
-  test.skipIf(isWindows())("does not include readme files that has no input-file:", async () => {
-    const actual = await buildState(
-      ["specification/no-input-file/readme.md"],
-      "test/fixtures/buildState/",
-    );
-
-    expect(actual).toEqual([new Map<string, ReadmeAffectedTags>(), []]);
-  });
 });