ReleaseNotes: don't bother mentioning GNU TLS

It's not like we're using for anything critical at the moment, and we
did not upgrade because there were new goodies, but we upgraded to
unbreak `gpg.exe` in the 32-bit version of Git for Windows, so...

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

ReleaseNotes.md

@@ -55,7 +55,6 @@ Also, the option to override the branch name used by `git init` for the initial
 * Git for Windows' installer learned to [let users override the default branch used by `git init`](https://github.com/git-for-windows/build-extra/pull/307).
 * [The installer size was reduced](https://github.com/git-for-windows/build-extra/pull/309) by dropping a couple unneeded `.dll` files.
 * Comes with [cURL v7.73.0](https://curl.haxx.se/changes.html#7_73_0).
-* Comes with [GNU TLS v3.6.15](https://lists.gnupg.org/pipermail/gnutls-help/2020-September/004669.html).
 
 ### Bug Fixes