[hostimage] No need to mark packages as auto since all debootstrap installed packages are fundamental and will not be removed

[qiluo-msft]

- Why I did it
Originally this line is used to mark all previously installed packages (deboostrap installed) as auto, so later if no other packages depend on anyone of them, it will be auto removed. Seems we gained little from this line, so let's remove it.

- How I did it

- How to verify it
Check the build log after sudo LANG=C chroot ./fsroot apt-get -y autoremove and the removed packages are unchanged.

The following packages will be REMOVED:
  binutils binutils-common binutils-x86-64-linux-gnu cpp cpp-8 gcc-8 libasan5
  libatomic1 libbinutils libc-dev-bin libc6-dev libcc1-0 libexpat1-dev
  libgcc-8-dev libgomp1 libisl19 libitm1 liblsan0 libmpc3 libmpfr6 libmpx2
  libquadmath0 libtsan0 libubsan1 linux-libc-dev
0 upgraded, 0 newly installed, 25 to remove and 5 not upgraded.

- Which release branch to backport (provide reason below if selected)

• 201811
• 201911
• 202006

- Description for the changelog

- A picture of a cute animal (not mandatory but encouraged)

[qiluo-msft]

Retest vsimage please