Revert "increase default context length to 4096 (#10364)"

This reverts commit 424f648632.

server/sched_test.go

@@ -148,7 +148,6 @@ func newScenarioRequest(t *testing.T, ctx context.Context, modelName string, est
 		successCh:       make(chan *runnerRef, 1),
 		errCh:           make(chan error, 1),
 	}
-	b.req.opts.NumCtx = 4096
 	b.srv = &mockLlm{estimatedVRAM: estimatedVRAM, estimatedVRAMByGPU: map[string]uint64{"": estimatedVRAM}}
 	return b
 }