gnu: olm: Drop custom ‘lib-’ prefix.

* gnu/packages/crypto.scm (olm): New variable, renamed from…
(libolm): …this one, which is now a DEPRECATED-PACKAGE alias of olm.
Adjust all users.
[synopsis, description]: Adjust.  Capitalise proper nouns.
(python-olm)[description]: Remove implementation detail.

gnu/packages/messaging.scm

@@ -2380,7 +2380,7 @@ QMatrixClient project.")
            curl
            json-modern-cxx
            libevent
-           libolm
+           olm
            libsodium
            openssl
            spdlog
@@ -2463,7 +2463,7 @@ for the Matrix protocol.  It is built on to of @code{Boost.Asio}.")
            json-modern-cxx
            libevent
            libnice                      ; for voip
-           libolm
+           olm
            lmdb
            lmdbxx
            mtxclient
@@ -2884,7 +2884,7 @@ validating international phone numbers.")
            libgcrypt
            libgee
            libhandy
-           libolm
+           olm
            libphonenumber
            modem-manager
            pidgin