remove redundant torch 1.5.0 uninstall/install from Dockerfile

Summary: Was needed when we had a dependency to torch 1.5.0-nightly. Not needed anymore as torch 1.5.0 has been released.

Reviewed By: tierex

Differential Revision: D21416939

fbshipit-source-id: 0caf00b7be5b3da18a84af2722dc6b55c944acd3

Author: Kiuk Chung

Dockerfile

@@ -3,8 +3,6 @@ FROM pytorch/pytorch:1.5-cuda10.1-cudnn7-runtime
 # install torchelastic
 WORKDIR /opt/torchelastic
 COPY . .
-RUN pip uninstall -y -qqq torch
-RUN pip install --progress-bar off torch==1.5.0
 RUN pip install -v .
 
 WORKDIR /workspace