feat(travis): provide curtailed .travis.yml for reference purposes

Originally was this:

```
feat(travis): ensure `.travis.yml` is always removed
```

However, took this comment into account:

* saltstack-formulas/consul-formula#52 (comment)

But still removing `.travis.yml` for the `ssf-formula`.

ssf/config/formulas.sls

@@ -101,10 +101,12 @@ prepare-git-branch-for-{{ formula }}:
 {#-           Or if the file is `libsaltcli.jinja` and `use_libsaltcli` is `False` #}
 {#-           Likewise, if running the state for TOFS files when `use_tofs` is `False` #}
 {#-           Also remove the local `CONTRIBUTING` file to use the org-level file instead #}
+{#-           Furthermore, remove `.travis.yml` for the `ssf-formula` #}
 {%-           if (semrel_file == '.cirrus.yml' and not use_cirrus_ci) or
                  (semrel_file == 'formula/libsaltcli.jinja' and not use_libsaltcli) or
                  (semrel_file in ['docs/TOFS_pattern.rst', 'formula/libtofs.jinja'] and not use_tofs) or
-                 (semrel_file in ['docs/CONTRIBUTING.rst'] and formula not in ['.github', 'ssf-formula'])
+                 (semrel_file in ['docs/CONTRIBUTING.rst'] and formula not in ['.github', 'ssf-formula']) or
+                 (semrel_file in ['.travis.yml'] and formula in ['ssf-formula'])
 %}
 {%-             set add_or_rm = ['rm', 'remove', 'absent'] %}
 {%-           endif %}

ssf/files/default/.travis.yml

@@ -1,6 +1,15 @@
 # -*- coding: utf-8 -*-
 # vim: ft=yaml
 ---
+################################################################################
+# NOTE: This file is UNMAINTAINED; it is provided for references purposes only.
+#       No guarantees are tendered that this structure will work after 2020.
+################################################################################
+# * https://en.wikipedia.org/wiki/Travis_CI:
+#   - "... free open-source plans were removed in [sic] the end of 2020"
+#   - https://blog.travis-ci.com/2020-11-02-travis-ci-new-billing
+#   - https://ropensci.org/technotes/2020/11/19/moving-away-travis/
+################################################################################
 {%- from tplroot ~ "/libcimatrix.jinja" import format_ci_matrix with context %}
 
 {%- macro format_allow_failures(use_single_job_for_linters) %}
@@ -104,8 +113,10 @@ script:
 ## Stages and jobs matrix
 stages:
   - test
-  - name: 'release'
-    if: 'branch = master AND type != pull_request'
+  # # As part of the switch away from Travis CI, ensure that the `release` stage
+  # # is not run inadvertently
+  # - name: 'release'
+  #   if: 'branch = master AND type != pull_request'
 jobs:
   {{- format_allow_failures(travis.use_single_job_for_linters) }}
   include:

ssf/files/tofs_docker-formula/.travis.yml

@@ -1,6 +1,15 @@
 # -*- coding: utf-8 -*-
 # vim: ft=yaml
 ---
+################################################################################
+# NOTE: This file is UNMAINTAINED; it is provided for references purposes only.
+#       No guarantees are tendered that this structure will work after 2020.
+################################################################################
+# * https://en.wikipedia.org/wiki/Travis_CI:
+#   - "... free open-source plans were removed in [sic] the end of 2020"
+#   - https://blog.travis-ci.com/2020-11-02-travis-ci-new-billing
+#   - https://ropensci.org/technotes/2020/11/19/moving-away-travis/
+################################################################################
 ## Machine config
 os: 'linux'
 arch: 'amd64'
@@ -32,8 +41,10 @@ script:
 ## Stages and jobs matrix
 stages:
   - test
-  - name: 'release'
-    if: 'branch = master AND type != pull_request'
+  # # As part of the switch away from Travis CI, ensure that the `release` stage
+  # # is not run inadvertently
+  # - name: 'release'
+  #   if: 'branch = master AND type != pull_request'
 jobs:
   include:
     ## Define the test stage that runs the linters (and testing matrix, if applicable)