chore: switch to Eask for package testing

This commit removes some files that are no longer needed for testing
the package, such as the files in the ./test directory which are
already covered by Eask itself.

BREAKING CHANGE: test files no longer exists

Eask

@@ -0,0 +1,14 @@
+(package "ox-gemini"
+         "0.2.0"
+         "Output gemini formatted documents from org-mode")
+
+(website-url "https://labs.phundrak.com/phundrak/ox-gemini")
+(keywords "lisp" "org-mode")
+
+(package-file "ox-gemini.el")
+
+(script "test" "echo \"Error: no test specified\" && exit 1")
+
+(source "gnu")
+
+(depends-on "emacs" "26.1")