Remove .github folder

Issue and merge request templates have been adjusted in the gitlab
settings to contain roughly the same information.

.github/ISSUE_TEMPLATE.md

-<!--
-    When making a bug report, please consider the following notes.
-
-    * Is the error already described here?
-        https://postmarketos.org/troubleshooting
-    * pmbootstrap:
-        * Attach the output of "pmbootstrap log" in this issue
-        * In case "pmbootstrap log" is not helpful, try running the command
-          which causes the error with "-v" (e.g. "pmbootstrap -v install")
-    * osk-sdl:
-        * Please report here: https://github.com/postmarketOS/osk-sdl/issues
-    * kernel issue:
-        * Check "dmesg" on the device and attach the output if it could be
-          useful.
-    * X11/Wayland/other userspace program issue:
-        * Check "logread" on the device and attach the output if it could be
-          useful.
-
-    Please insert your text below and feel free to delete this big comment
-    block after reading.
--->

.github/PULL_REQUEST_TEMPLATE.md

-<!--
-    We appreciate that you are about to create a pull request (PR)!
-
-    In order to get it tested (code change), reviewed and merged quickly,
-    please take a look at the following notes.
-
-    1. We only merge PRs that pass all tests:
-        * As soon as you create the PR, automatic tests will run with Travis CI
-        * Come back later to see if everything passed
-        * Click on the failed test icon to see why it failed and try to fix it
-        * In case Travis failed for a reason not related to your changes (e.g.
-          network issues or missing documentation), push an empty commit:
-            git commit --allow-empty -m 'run tests again'
-        * You can run the tests locally as well:
-            test/static_code_analysis.sh
-            test/testcases_fast.sh
-    2. All commits in the PR will get squashed into one (so you don't need to
-       do that).
-    3. New device:
-        * Is it documented in the wiki?
-    4. Code change:
-        * Depending on the complexity of the change, consider structuring your
-          PR message with headlines (### headline) in sections, e.g.:
-            * Overview (context and short description of the change)
-            * Usage example (cli output)
-            * Changes (detailed list of every change made)
-            * How to test
-        * Add 'Close #nnnn' or 'Fixes #nnnn' at the bottom to automatically
-          close issue nnnn as soon as your PR gets merged.
-
-    Please insert your text before the --- line, feel free to delete this big
-    comment block after reading.
--->
----
-[x] Merge on GitHub (see <https://postmarketos.org/merge>)