Remove explicit reference to the Generic.Files.LineEndings sniff

[aadmathijssen]

This PR removes the explicit inclusion of the Generic.Files.LineEndings sniff.

This is unnecessary, as this sniff is already included via the PSR12 ruleset:

    <!-- All PHP files MUST use the Unix LF (linefeed) line ending only. -->
    <rule ref="Generic.Files.LineEndings">
        <properties>
            <property name="eolChar" value="\n"/>
        </properties>
    </rule>

Note that the PSR12 ruleset explicitly specifies a value for the eolChar property, whereas the ISAAC ruleset did not. However, this doesn't make a difference, since the \n value is the default value of that property.