d/control: Drop Priority of libcap2

The intention is to reduce Priority to "optional". The field is dropped, as
this is the source package's Priority, and would therefore be redundant.

debian/control

@@ -31,7 +31,6 @@ Description: POSIX 1003.1e capabilities (utilities)
  This package contains additional utilities.
 
 Package: libcap2
-Priority: important
 Architecture: linux-any
 Multi-Arch: same
 Pre-Depends: ${misc:Pre-Depends}