[warm-reboot] Remove warmboot file path that overrides the default path

[shi-su]

- Why I did it
The sai.profile file in kvm images overrides the warmboot file with path /var/cache/sai_warmboot.bin. Since the directory /var/cache is not mounted in syncd, it will be cleared in an image upgrade, the warm-reboot image upgrade will fail if the file is put in the directory.

Fix #6183

- How I did it
Remove the path that overrides the default path. The warmboot file path will then be the default value /var/warmboot/sai-warmboot.bin. Since /var/warmboot/ is mounted by /host/warmboot/ in the host, it could survive an image upgrade.

- How to verify it
Tested warm reboot upgrading kvm image locally.

- 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)

[kcudnik]

@shi-su @lguohan Just to clarify, if we have right now in production image running this profile, it will write on warm shutdown to /var/cache but new image with this PR will not pick up that file, since it will use default value which is "/var/warmboot/sai-warmboot.bin"

from the other hand, i see that this changes are only for VS ?

[shi-su]

@shi-su @lguohan Just to clarify, if we have right now in production image running this profile, it will write on warm shutdown to /var/cache but new image with this PR will not pick up that file, since it will use default value which is "/var/warmboot/sai-warmboot.bin"

from the other hand, i see that this changes are only for VS ?

I only found this profile for VS, real devices should just use the default path. So devices in production should not be affected.