CI: Remove GCC 6 pipeline

libeigen/eigen!2323

Co-authored-by: Rasmus Munk Larsen <rmlarsen@gmail.com>

ci/build.linux.gitlab-ci.yml

diff --git a/ci/build.linux.gitlab-ci.yml b/ci/build.linux.gitlab-ci.yml
index fdbb59a..198c01f 100644
--- a/ci/build.linux.gitlab-ci.yml
+++ b/ci/build.linux.gitlab-ci.yml
@@ -26,17 +26,6 @@
     EIGEN_CI_TARGET_ARCH: x86_64
     EIGEN_CI_CROSS_TARGET_TRIPLE: x86_64-linux-gnu
 
-# GCC-6 (minimum on Ubuntu 18.04)
-build:linux:cross:x86-64:gcc-6:default:
-  extends: .build:linux:cross:x86-64
-  image: ubuntu:18.04
-  variables:
-    EIGEN_CI_C_COMPILER: gcc-6
-    EIGEN_CI_CXX_COMPILER: g++-6
-    EIGEN_CI_CROSS_INSTALL: g++-6-x86-64-linux-gnu
-    EIGEN_CI_CROSS_C_COMPILER: x86_64-linux-gnu-gcc-6
-    EIGEN_CI_CROSS_CXX_COMPILER: x86_64-linux-gnu-g++-6
-
 # GCC-10 (stable recent version)
 build:linux:cross:x86-64:gcc-10:default:
   extends: .build:linux:cross:x86-64

ci/test.linux.gitlab-ci.yml

diff --git a/ci/test.linux.gitlab-ci.yml b/ci/test.linux.gitlab-ci.yml
index 3461f97..f7f3121 100644
--- a/ci/test.linux.gitlab-ci.yml
+++ b/ci/test.linux.gitlab-ci.yml
@@ -21,24 +21,6 @@
     EIGEN_CI_TARGET_ARCH: x86_64
     EIGEN_CI_CROSS_TARGET_TRIPLE: x86_64-linux-gnu
 
-# GCC-6 (minimum on Ubuntu 18.04)
-.test:linux:x86-64:gcc-6:default:
-  extends: .test:linux:x86-64
-  image: ubuntu:18.04
-  needs: [ build:linux:cross:x86-64:gcc-6:default ]
-  variables:
-    EIGEN_CI_INSTALL: g++-6
-
-test:linux:x86-64:gcc-6:default:official:
-  extends: .test:linux:x86-64:gcc-6:default
-  variables:
-    EIGEN_CI_CTEST_LABEL: Official
-
-test:linux:x86-64:gcc-6:default:unsupported:
-  extends: .test:linux:x86-64:gcc-6:default
-  variables:
-    EIGEN_CI_CTEST_LABEL: Unsupported
-
 # GCC-10 (modern stable)
 .test:linux:x86-64:gcc-10:default:
   extends: .test:linux:x86-64