Revert "Pass SwiftFormatRules sources as inputs to generate-pipeline-plugin."

This reverts commit f3b6192.

Author: DougGregor

Plugins/generate-pipeline-plugin/GeneratePipelinePlugin.swift

@@ -49,10 +49,6 @@ struct GeneratePipelinePlugin: BuildToolPlugin {
       .appending("GeneratedSources")
       .appending(generatedSourceName)
 
-    let rulesSources =
-      (try context.package.targets(named: ["SwiftFormatRules"]).first as? SwiftSourceModuleTarget)?
-      .sourceFiles.map(\.path) ?? []
-
     return [
       .buildCommand(
         displayName: "Generating \(generatedSourceName) for \(target.name)",
@@ -65,7 +61,6 @@ struct GeneratePipelinePlugin: BuildToolPlugin {
           "--target",
           target.name,
         ],
-        inputFiles: rulesSources,
         outputFiles: [outputFile]
       )
     ]