remove prepare cleanWs step because exec error

[simonJi2018]

No description provided.

[lguohan]

I am seeing this for all build. not sure why we need to treat this differently.

broadcom/buildimage-brcm-all-pr/Jenkinsfile:                step([$class: 'WsCleanup'])
broadcom/buildimage-brcm-all-released-pr/Jenkinsfile:                step([$class: 'WsCleanup'])
broadcom/buildimage-brcm-all/Jenkinsfile:                step([$class: 'WsCleanup'])
broadcom/buildimage-brcm-buster/Jenkinsfile:                step([$class: 'WsCleanup'])
generic/buildimage-baseimage-pr/Jenkinsfile:                step([$class: 'WsCleanup'])
innovium/buildimage-invm-201811-rpc/Jenkinsfile:                step([$class: 'WsCleanup'])
innovium/buildimage-invm-201811/Jenkinsfile:                step([$class: 'WsCleanup'])
innovium/buildimage-invm-201911-rpc/Jenkinsfile:                step([$class: 'WsCleanup'])
innovium/buildimage-invm-201911/Jenkinsfile:                step([$class: 'WsCleanup'])
innovium/buildimage-invm-all-rpc/Jenkinsfile:                step([$class: 'WsCleanup'])
innovium/buildimage-invm-all/Jenkinsfile:                step([$class: 'WsCleanup'])
mellanox/buildimage-mlnx-201811-rpc/Jenkinsfile:                step([$class: 'WsCleanup'])
mellanox/buildimage-mlnx-201911-rpc/Jenkinsfile:                step([$class: 'WsCleanup'])
mellanox/buildimage-mlnx-all-pr/Jenkinsfile:                step([$class: 'WsCleanup'])
mellanox/buildimage-mlnx-all-released-pr/Jenkinsfile:                step([$class: 'WsCleanup'])
mellanox/buildimage-mlnx-all-rpc/Jenkinsfile:                step([$class: 'WsCleanup'])
mellanox/buildimage-mlnx-all/Jenkinsfile:                step([$class: 'WsCleanup'])
mellanox/buildimage-mlnx-bmtor-rpc/Jenkinsfile:                step([$class: 'WsCleanup'])
mellanox/buildimage-mlnx-bmtor/Jenkinsfile:                step([$class: 'WsCleanup'])
nephos/buildimage-nps-all/Jenkinsfile:                step([$class: 'WsCleanup'])
vs/buildimage-vs-all-pr/Jenkinsfile:                step([$class: 'WsCleanup'])
vs/buildimage-vs-image-released-pr/Jenkinsfile:                step([$class: 'WsCleanup'])