init-system-helpers: upgrade 1.62 -> 1.63

init-system-helpers: upgrade 1.62 -> 1.63

Changelog:
==========
  * Remove constraints unnecessary since buster
    * init-system-helpers: Drop versioned constraint on perl-base in Depends.
    * init: Drop versioned constraint on init-system-helpers in Depends.

  * t/helpers.pm: use installed version of deb-systemd-helper if
    TEST_INSTALLED is set
  * add DPKG_ROOT support (Closes: #983421)

  * Add additional error checking on write operations.
    The 'close()' call can fail on both read and write - while the read is
    usually relatively benign, for the write counter part can include "fun"
    errors. Most of these would most likely be persistent issues, but it makes
    sense to detect errors as early possible.

  * service: use 'grep -F' instead of 'egrep'
    'egrep' and 'fgrep' have been deprecated in GNU grep since 2007, and in
    current post 3.7 Git they have been made to emit obsolescence warnings.
    The occurrence in 'service' uses a non-regex argument, so switch to 'grep
    -F' instead of '-E'.

Signed-off-by: Wang Mingyu <wangmy@fujitsu.com>
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>