Revert the changes for NNPACK build issue (#13913)

This patch undoes the change that was put in place to prevent the build and installation of NNPACK from failing due to a renaming of the default branch to main by the NNPACK external dependency cpuinfo.

See #13871

The issue has been fixed at the source by PR #214 which is now merged in to NNPACK, so the change to `ubuntu_install_nnpack.sh` is no longer required:

Maratyszcza/NNPACK#214

Author: Liam-Sturge

docker/install/ubuntu_install_nnpack.sh

@@ -26,7 +26,7 @@ git clone https://github.com/Maratyszcza/NNPACK NNPACK
 git clone https://github.com/Maratyszcza/pthreadpool  NNPACK/pthreadpool
 
 # Use specific versioning tag.
-(cd NNPACK && sed -i 's/GIT_TAG master/GIT_TAG main/g' ./cmake/DownloadCpuinfo.cmake && git checkout 1e005b0c2)
+(cd NNPACK && git checkout 70a77f485)
 (cd NNPACK/pthreadpool && git checkout 13da0b4c)
 
 mkdir -p NNPACK/build