No need to define our own `com_dotnet_object_properties` as empty hash,
since we can use `zend_empty_array` instead as of PHP 7.3.0.

Cf. <https://github.com/php/php-src/pull/3672#issuecomment-440467704>.

* PHP-7.2:
  Fix #77177: Serializing or unserializing COM objects crashes

Firstly, we avoid returning NULL from the get_property handler, but
instead return an empty HashTable, which already prevents the crashes.
Secondly, since (de-)serialization obviously makes no sense for COM,
DOTNET and VARIANT objects (at least with the current implementation),
we prohibit it right away.

* PHP-7.2:
  Fix callbacks
  bump version

The signatures wasn't synced in 7.0

The $Id$ keywords were used in Subversion where they can be substituted
with filename, last revision number change, last changed date, and last
user who changed it.

In Git this functionality is different and can be done with Git attribute
ident. These need to be defined manually for each file in the
.gitattributes file and are afterwards replaced with 40-character
hexadecimal blob object name which is based only on the particular file
contents.

This patch simplifies handling of $Id$ keywords by removing them since
they are not used anymore.