Remove native x86_64 test run

We are removing this since we have been doing it all along with a split-job since we exploded CI back in b5b5247279

.gitlab-ci.yml

@@ -1111,12 +1111,6 @@ prepare-cache:qemu:
     - .gitlab/build-test.sh --jobs $((cpus + 1)) --maxload ${cpus} --with-arch ${ARCH} --with-debian stretch --with-debian-mirror http://ftp.de.debian.org/debian/ --with-project-path ${CI_PROJECT_DIR} --with-chroot-path /tmp/racket-${ARCH}-${CI_COMMIT_SHORT_SHA}-chroot --with-qemu-path $INSTALL_DIR
   dependencies:
     - prepare-cache:qemu
-    
-test:native:x86_64:
-  extends: .preparearch
-  variables:
-    ARCH: "x86_64"
-    INSTALL_DIR: $CI_PROJECT_DIR/install
 
 test:native:armv7l:
   extends: .preparearch