ci: stop using the "big" Gitlab CI runners (MR 5565)

These runners seem to no longer be available to contributors who submit MRs from their personal forks.

I reported this to Gitlab here: https://gitlab.com/gitlab-org/gitlab/-/issues/483771

This reverts commit e065a311.
This reverts commit c4c6a222.

.gitlab-ci.yml

@@ -125,8 +125,6 @@ mr-settings:
 # build changed aports
 .build:
   stage: build
-  tags:
-    - saas-linux-large-amd64
   rules:
     - if: $CI_PIPELINE_SOURCE == "merge_request_event" || $CI_COMMIT_REF_PROTECTED == "false"
   before_script:
@@ -152,8 +150,6 @@ build-x86:
 
 build-aarch64:
   extends: .build
-  tags:
-    - saas-linux-large-arm64
   script:
     - .ci/build-aarch64.sh
 
@@ -174,9 +170,6 @@ build-riscv64:
 
 auto-update:
   stage: autoupdate
-  # We build packages before merging too
-  tags:
-    - saas-linux-large-amd64
   rules:
     # This variable is set in the scheduled pipeline configuration. It should be a space separated list of
     # package names to update.