d/control: Reduce priority of libnfsidmap1 to optional as well

Since Debian policy version 4.0.1, shared libraries should have
priority optional even if they have reverse-dependencies of higher
priority.

debian/changelog

@@ -8,6 +8,7 @@ nfs-utils (1:2.5.4-1~exp6) UNRELEASED; urgency=medium
   * lintian: Refresh lintian-overrides
   * d/control: Make nfs-kernel-server directly Recommend python3, as
     lintian wants
+  * d/control: Reduce priority of libnfsidmap1 to optional as well
 
  -- Ben Hutchings <benh@debian.org>  Wed, 19 Jan 2022 22:41:22 +0100
 

debian/control

@@ -55,7 +55,6 @@ Description: header files and docs for libnfsidmap
  of the form user@domain) and local uid's and gid's.
 
 Package: libnfsidmap1
-Priority: standard
 Section: libs
 Architecture: any
 Multi-Arch: same