refactor: remove nofallback parameter

Remove the nofallback input parameter as it's no longer needed. The action
now assumes that a builder is already configured and available.

Changes:
- Remove nofallback from action.yml inputs
- Remove nofallback from Inputs interface and getInputs function
- Update tests to remove nofallback references
- Also remove setup-only and buildx-version from action.yml (already removed from code)

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/__tests__/blacksmith-builder.test.ts

@@ -34,7 +34,6 @@ describe('reportBuildMetrics', () => {
   beforeEach(() => {
     jest.clearAllMocks();
     mockInputs = {
-      nofallback: false,
       setupOnly: false,
       platforms: []
     };

src/context.ts

@@ -57,7 +57,6 @@ export interface Inputs {
   target: string;
   ulimit: string[];
   'github-token': string;
-  nofallback: boolean;
 }
 
 export async function getInputs(): Promise<Inputs> {
@@ -94,8 +93,7 @@ export async function getInputs(): Promise<Inputs> {
     tags: Util.getInputList('tags'),
     target: core.getInput('target'),
     ulimit: Util.getInputList('ulimit', {ignoreComma: true}),
-    'github-token': core.getInput('github-token'),
-    nofallback: core.getBooleanInput('nofallback')
+    'github-token': core.getInput('github-token')
   };
 }
 

src/main.ts

@@ -21,10 +21,10 @@ import {Metric_MetricType} from '@buf/blacksmith_vm-agent.bufbuild_es/stickydisk
 
 async function assertBuildxAvailable(toolkit: Toolkit): Promise<void> {
   if (!(await toolkit.buildx.isAvailable())) {
-    core.setFailed(`Docker buildx is required. Please use setup-docker-builder action or setup-buildx-action to configure buildx.`);
+    core.setFailed(`Docker buildx is required. Please use setup-docker-builder action to configure buildx.`);
     throw new Error('Docker buildx is not available');
   }
-  
+
   await core.group(`Buildx version`, async () => {
     await toolkit.buildx.printVersion();
   });
@@ -145,7 +145,6 @@ actionsToolkit.run(
         }
       });
 
-
       const args: string[] = await context.getArgs(inputs, toolkit);
       args.push('--debug');
       core.debug(`context.getArgs: ${JSON.stringify(args)}`);