Remove the Release 1 pipeline files; point everything at Release 2

new_docker_build.sh and rpmbuild/make_rpm_ubuntu26.py (Release 1
validation-scope driver/producer) did not belong to this branch; their
functional callers are adapted to the Release 2 files:

- rpmbuild/make_rpm_ubuntu26_release2.py: PIPELINE_FILES now packages
  new_docker_build_release2.sh and make_rpm_ubuntu26_release2.py.
- jenkins-ci-rme/jenkins_builder_ubuntu26.sh: runs
  make_rpm_ubuntu26_release2.py with -DBUILD_RTI=ON and the Release 2
  target list (--build_targets; a full-tree build is not possible on
  this tree); staging tar also excludes ./build4*.
- jenkins-ci-rme/release-16-10-2026.sh (local dry run): calls
  new_docker_build_release2.sh; derives the pipeline root from the tree
  layout and exports MIGRATE_PIPELINE_ROOT; uses the prebuilt image when
  present, otherwise the driver installs deps in-container (the R1
  --build-prebuilt-image option does not exist in the R2 driver).
- jenkins-ci-rme/jenkins/Jenkinsfile: coverage stage runs the R2 driver
  with MIGRATE_PIPELINE_ROOT exported (wins over the checked-in .envrc,
  which carries a host-specific path).
- Doc/comment updates: Dockerfile header, install_arcgis.sh, publisher,
  Jenkinsfile descriptions, jenkins-ci-rme/README.md, README.md.

Remaining references to the old names are only in historical migration
reports, which are left as-is.

qt6-after/qt6-migrated-legatus/Dockerfile

@@ -1,8 +1,9 @@
-# Prebuilt build image for the release validation-scope branch
+# Prebuilt build image for the Release 2 branch
 # (Ubuntu 26.04 + Qt6 + all dependencies for the legatus release build).
 #
-# Built by new_docker_build.sh --build-prebuilt-image, which passes the
-# package list and Qt settings as build args (see build_prebuilt_image()).
+# Build with (the APT package list mirrors the in-container install list of
+# new_docker_build_release2.sh):
+#   docker build --build-arg APT_PACKAGES="<space-separated packages>" -t <image> .
 
 FROM ubuntu:26.04