refactor(language-service): remove unnecessary size check (#32587)

Presumably, the size of the results array was checked so that a TS
source file wouldn't have to be created if there were no diagnostics.
However, it is very likely that a TS program already has the
`ts.SourceFile` for file when diagnostics are queried. This removal is
just to make the function a minimal amount simpler.

PR Close #32587

packages/language-service/src/language_service.ts

@@ -49,9 +49,6 @@ class LanguageServiceImpl implements LanguageService {
     if (declarations && declarations.length) {
       results.push(...getDeclarationDiagnostics(declarations, analyzedModules));
     }
-    if (!results.length) {
-      return [];
-    }
     const sourceFile = fileName.endsWith('.ts') ? this.host.getSourceFile(fileName) : undefined;
     return uniqueBySpan(results).map(d => ngDiagnosticToTsDiagnostic(d, sourceFile));
   }