Drop legacy dev/ dependencies

We can't rely on python 3.3 being globally available anymore.
GitHub's Windows 2019 runner is the last one, supporting it.

Hence moving forward to use UnitTesting package for upstream and downstream
unit tests as it runs them on ST's plugin_hosts.

This commit therefore drops obsolete files no longer needed for testing.

Author: deathaxe

.gitattributes

@@ -5,8 +5,6 @@
 .gitattributes export-ignore
 
 # development utilities
-/dev/ export-ignore
-.travis.yml export-ignore
 tox.ini export-ignore
 
 # unittests

.gitignore

@@ -1,5 +1,4 @@
 # development dependencies
-dev/.lint-deps/
 .venv*/
 
 # linter cache