Doc: remove old release notes about systemd and riscv changes

doc/release-notes.md

@@ -2,7 +2,7 @@ Bitcoin Core version 0.18.1 is now available from:
 
   <https://bitcoincore.org/bin/bitcoin-core-0.18.1/>
 
-This is a new major version release, including new features, various bug
+This is a new minor version release, including new features, various bug
 fixes and performance improvements, as well as updated translations.
 
 Please report bugs using the issue tracker at GitHub:
@@ -47,19 +47,6 @@ built using Qt 5.9.x, which doesn't support versions of macOS older than
 10.10. Additionally, Bitcoin Core does not yet change appearance when
 macOS "dark mode" is activated.
 
-In addition to previously-supported CPU platforms, this release's
-pre-compiled distribution also provides binaries for the RISC-V
-platform.
-
-If you are using the `systemd` unit configuration file located at
-`contrib/init/bitcoind.service`, it has been changed to use
-`/var/lib/bitcoind` as the data directory instead of
-`~bitcoin/.bitcoin`. When switching over to the new configuration file,
-please make sure that the filesystem on which `/var/lib/bitcoind` will
-exist has enough space (check using `df -h /var/lib/bitcoind`), and
-optionally copy over your existing data directory. See the [systemd init
-file section](#systemd-init-file) for more details.
-
 Known issues
 ============