Remove leftover TINC CI support

Commit cd733c64 removed the TINC
tests from the CI pipeline, but these files were seemingly left
behind and made dead code. Remove.
Reviewed-by: NAshwin Agrawal <aagrawal@pivotal.io>

concourse/tasks/gpdb_src_tinc_packaging.yml

-platform: linux
-image_resource:
-  type: docker-image
-inputs:
-  - name: gpdb_src
-outputs:
-  - name: rc_bin_gpdb
-run:
-  path: gpdb_src/concourse/scripts/gpdb_src_tinc_packaging.bash
-params:
-  GPDB_SRC_TAR_GZ: rc_bin_gpdb/greenplum-db-VERSION_OS-x86_64_src.tar.gz

concourse/tasks/run_tinc.yml

-platform: linux
-inputs:
- - name: ccp_src
- - name: cluster_env_files
-run:
-  path: bash
-  args:
-  - -c
-  - |
-    set -ex
-    ccp_src/scripts/setup_ssh_to_cluster.sh
-    ssh -t mdw "$CUSTOM_ENV bash /home/gpadmin/gpdb_src/concourse/scripts/run_tinc_test.sh \"$TINC_TARGET\""

concourse/tasks/tinc_gpdb.yml

-platform: linux
-image_resource:
-  type: docker-image
-inputs:
-  - name: gpdb_src
-  - name: bin_gpdb
-outputs:
-params:
-  MAKE_TEST_COMMAND: ""
-  BLDWRAP_POSTGRES_CONF_ADDONS: ""
-  TEST_OS: ""
-  CONFIGURE_FLAGS: ""
-run:
-  path: gpdb_src/concourse/scripts/tinc_gpdb.bash