(not for master): CI: disable armhf, riscv64, x86 (MR 5070)

The staging repository isn't being built for these.

.gitlab-ci.yml

@@ -145,11 +145,6 @@ build-x86_64:
   script:
     - .ci/build-x86_64.sh
 
-build-x86:
-  extends: .build
-  script:
-    - .ci/build-x86.sh
-
 build-aarch64:
   extends: .build
   script:
@@ -160,16 +155,6 @@ build-armv7:
   script:
     - .ci/build-armv7.sh
 
-build-armhf:
-  extends: .build
-  script:
-    - .ci/build-armhf.sh
-
-build-riscv64:
-  extends: .build
-  script:
-    - .ci/build-riscv64.sh
-
 auto-update:
   stage: autoupdate
   rules: