add missing BuildRequires: systemd-rpm-macros

[corporate-gadfly]

On SLES, the package uses %service_del_preun and %service_del_postun macros but doesn't declare systemd-rpm-macros as a build dependency.

This causes the macros to be incorrectly expanded or missing, resulting in scriptlet failures during package removal on SLES15:

error: %preun(openvox-server) scriptlet failed, exit status 1
/var/tmp/rpm-tmp.XXX: line 1: fg: no job control

Adding the BuildRequires ensures the macros are properly defined during package build.

[corporate-gadfly]

@nmburgan Thoughts on using following diff in Dockerfile in openvox-server:

diff --git a/Dockerfile b/Dockerfile
index 74b2df1cd1..7634b50a6a 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -4,8 +4,14 @@ RUN apt-get update && \
     apt-get install -y --no-install-recommends \
       openjdk-17-jdk-headless \
       rpm \
+      cpio \
     && rm -rf /var/lib/apt/lists/*
 
+# Extract the RPM macros to resolve the expansion of macros on SLES
+RUN wget -q https://rpmfind.net/linux/opensuse/distribution/leap/16.0/repo/oss/noarch/systemd-rpm-macros-26-160000.2.2.noarch.rpm -O /tmp/suse-macros.rpm && \
+    rpm2cpio /tmp/suse-macros.rpm | cpio -idmv -D / && \
+    rm /tmp/suse-macros.rpm
+
 RUN wget -q https://raw.githubusercontent.com/technomancy/leiningen/stable/bin/lein -O /usr/local/bin/lein && \
     chmod a+x /usr/local/bin/lein