chore(ci): remove firestore project and its reference

[iyabchen]

remove firestore project and its reference https://github.com/hashicorp/terraform-provider-google/issues/17775

Release Note Template for Downstream PRs (will be copied)

[modular-magician]

Hi there, I'm the Modular magician. I've detected the following information about your changes:

Diff report

Your PR generated some diffs in downstreams - here they are.

google provider: Diff ( 5 files changed, 3 insertions(+), 37 deletions(-)) google-beta provider: Diff ( 1 file changed, 11 deletions(-)) terraform-google-conversion: Diff ( 1 file changed, 7 deletions(-))

[modular-magician]

Tests analytics

Total tests: 3620 Passed tests: 3255 Skipped tests: 365 Affected tests: 0

Click here to see the affected service packages

all service packages are affected

$\textcolor{green}{\textsf{All tests passed!}}$ View the build log

[roaks3]

Fly-by comment: it looks like the prior usage was removed here https://github.com/GoogleCloudPlatform/magic-modules/pull/10168