Update PR template along practice (#254)

* remove automatically checked property

* Allow PR-submitters to self-document.

We don't ever use these, so allow submitters of PRs to self-document.

.github/pull_request_template.md

@@ -4,12 +4,10 @@
 
 <!-- If you are not submitting a new scheme, we suggest removing the following lines -->
 #### Manually checked properties
-<!-- These checkboxes serve for the maintainers of PQClean to verify your submission. Please do not check them yourself. -->
 
 * [ ] No stringification macros
 * [ ] Output-parameter pointers in functions are on the left
 * [ ] Negative return values on failure of API functions (within restrictions of FO transform).
-* [ ] `const` arguments are labeled as `const`
 * [ ] variable declarations at the beginning (except in `for (size_t i=...`)
 * Optional:
   * [ ] All integer types are of fixed size, using `stdint.h` types (including `uint8_t` instead of `unsigned char`)