buildx: remove install method from main module

Signed-off-by: CrazyMax <crazy-max@users.noreply.github.com>

__tests__/buildx/buildx.test.ts

@@ -88,14 +88,6 @@ describe('certsDir', () => {
   });
 });
 
-describe('install', () => {
-  it('acquires buildx v0.9.1', async () => {
-    const buildx = new Buildx({context: new Context()});
-    const buildxBin = await buildx.install('v0.9.1', tmpDir);
-    expect(fs.existsSync(buildxBin)).toBe(true);
-  }, 100000);
-});
-
 describe('isAvailable', () => {
   it('docker cli', async () => {
     const execSpy = jest.spyOn(exec, 'getExecOutput');