[PATCH v1 2/5] CI: drop Ubuntu 16.04

[Edwin Török <edwin.torok@xxxxxxxxxx>]

Ubuntu 16.04 is EoL on 2026-04-02.
It fails to build the emulator tests, probably due to a binutils that is too 
old:

```
gcc -m32 -march=i686 -DBUILD_ID -fno-strict-aliasing -std=gnu99 -Wall 
-Wstrict-prototypes -Wno-unused-but-set-variable -Wno-unused-local-typedefs 
-Werror -O2 -fomit-frame-pointer 
-D__XEN_INTERFACE_VERSION__=__XEN_LATEST_INTERFACE_VERSION__ 
-D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -mno-tls-direct-seg-refs -fno-pie 
-fno-exceptions -fno-asynchronous-unwind-tables -ffreestanding -nostdinc 
-I/builds/xen-project/people/edwintorok/xen/tools/tests/x86_emulator/../../../tools/firmware/include
 -fno-stack-protector -g0 -D_16 -mpclmul -mssse3 -mpclmul -ffixed-xmm0 -Os 
-DVEC_SIZE=16 -c ssse3-pclmul.c
/tmp/cchhD6n5.s: Assembler messages:
/tmp/cchhD6n5.s:202: Error: junk at end of line, first unrecognized character 
is `{'
/tmp/cchhD6n5.s:203: Error: junk at end of line, first unrecognized character 
is `{'
/tmp/cchhD6n5.s:205: Error: junk at end of line, first unrecognized character 
is `{'
```

Same test passes on Ubuntu 18.04.

Note: the minimum version of binutils might have to be updated.
Ubuntu 16.04 had version 2.26.1, which satisfies the >= 2.25 requirement
in the README, and yet it failed as shown above.

Signed-off-by: Edwin Török <edwin.torok@xxxxxxxxxx>
---
 automation/gitlab-ci/build.yaml | 10 ----------
 1 file changed, 10 deletions(-)

diff --git a/automation/gitlab-ci/build.yaml b/automation/gitlab-ci/build.yaml
index b69bad9202..41914cf898 100644
--- a/automation/gitlab-ci/build.yaml
+++ b/automation/gitlab-ci/build.yaml
@@ -615,16 +615,6 @@ fedora-41-x86_64-gcc-debug:
   variables:
     CONTAINER: fedora:41-x86_64
 
-ubuntu-16.04-x86_64-gcc:
-  extends: .gcc-x86-64-build
-  variables:
-    CONTAINER: ubuntu:16.04-x86_64
-
-ubuntu-16.04-x86_64-gcc-debug:
-  extends: .gcc-x86-64-build-debug
-  variables:
-    CONTAINER: ubuntu:16.04-x86_64
-
 ubuntu-18.04-x86_64-gcc:
   extends: .gcc-x86-64-build
   variables:
-- 
2.47.3