Revert "cloud-build: set HOME env variable."

This reverts commit b51a0c9a5b54f90b46fb74c93a3d0339a99c5e8e.

Reason for revert: Causes Cloud Build to fail: https://pantheon.corp.google.com/cloud-build/builds/933b93f5-1ceb-48d0-9f13-55e8b01b3e44?organizationId=433637338589&project=skia-public

Original change's description:
> cloud-build: set HOME env variable.
> 
> Bug: 993053
> Change-Id: I6069def4a063dbe7a4f8c6fe9cc5046d014e4f3c
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/247046
> Reviewed-by: Eric Boren <borenet@google.com>
> Commit-Queue: Joe Gregorio <jcgregorio@google.com>

TBR=borenet@google.com,jcgregorio@google.com

Change-Id: I311fe7240768ef0bf7015bdf0cd5a0e2aabe6c5c
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 993053
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/247051
Reviewed-by: Joe Gregorio <jcgregorio@google.com>
Commit-Queue: Joe Gregorio <jcgregorio@google.com>
2 files changed