remove RFCs/symbol_alias.md

[timotheecour]

as was requested, this removes the RFC md file I just added in favor of having it as an issue https://github.com/nim-lang/RFCs/issues/232

note that I still prefer an md file for complex RFC's like this one for those reasons:

• it's version controlled; unlike github issues
• makes it easier to collaborate on since it's version controlled (eg an RFC can get pull requests from others to improve/discuss it)
• makes it easier to comment on specific points via PR's or other means (eg: the comments I got from https://github.com/nim-lang/RFCs/pull/235; PR comments are easier to deal with than issue comments since you can comment on specific lines)

but then also Template.md should proably be removed too if we're not using md files for RFCS

[Araq]

but then also Template.md should proably be removed too if we're not using md files for RFCS

Yes and in fact for this repository "Pull requests" should be disabled.