Drop gcc:sid:i386 from GitLab CI

Building sid-i386 in Docker no longer works and we don't have a viable
alternative now, so dropping gcc:sid:i386 is our only option in this
very moment.

.gitlab-ci.yml

@@ -70,11 +70,6 @@ stages:
     - linux
     - amd64
 
-.linux-i386: &linux_i386
-  tags:
-    - linux
-    - i386
-
 .linux-stress-amd64: &linux_stress_amd64
   tags:
     - amd64
@@ -133,10 +128,6 @@ stages:
   image: "$CI_REGISTRY_IMAGE:debian-sid-amd64"
   <<: *linux_amd64
 
-.debian-sid-i386: &debian_sid_i386_image
-  image: "$CI_REGISTRY_IMAGE:debian-sid-i386"
-  <<: *linux_i386
-
 # openSUSE Tumbleweed
 
 .tumbleweed-latest-amd64: &tumbleweed_latest_amd64_image
@@ -837,30 +828,6 @@ unit:gcc:tarball:
     - schedules
     - tags
 
-# Jobs for regular GCC builds on Debian "sid" (i386)
-
-gcc:sid:i386:
-  variables:
-    CC: gcc
-    CFLAGS: "${CFLAGS_COMMON}"
-    EXTRA_CONFIGURE: "--with-libidn2"
-  <<: *debian_sid_i386_image
-  <<: *build_job
-
-system:gcc:sid:i386:
-  <<: *debian_sid_i386_image
-  <<: *system_test_job
-  needs:
-    - job: gcc:sid:i386
-      artifacts: true
-
-unit:gcc:sid:i386:
-  <<: *debian_sid_i386_image
-  <<: *unit_test_job
-  needs:
-    - job: gcc:sid:i386
-      artifacts: true
-
 # Jobs for debug GCC builds on openSUSE Tumbleweed (amd64)
 
 gcc:tumbleweed:amd64: