MDEV-5725: Don't install private mysql header files

Previously private/*.h where included in the package. These represent internal
mysqld structures that aren't guarenteed to provide a stable ABI.

There aren't intended to be used by embedded mysqld applications so
they have been removed.
Signed-off-by: Daniel Black <daniel.black@au.ibm.com>

debian/libmariadbclient-dev.install

 usr/bin/mysql_config
 usr/include/mariadb
-usr/include/mysql/*
+usr/include/mysql/*.h
+usr/include/mysql/psi/*.h
 usr/lib/*/libmariadb.so
 usr/lib/*/libmariadbclient.a
 usr/lib/*/libmysqlservices.a