pango-sys: Drop v1_36_7 feature

[ignatenkobrain]

It is not handled anywhere, so it would fall back into 1.36 which is default.

[EPashkin]

Restarting CI

[EPashkin]

@ignatenkobrain, @GuillaumeGomez I was careless when checking, it really used in PangoAnalysis for flags.

    <constant name="ANALYSIS_FLAG_IS_ELLIPSIS" value="2" c:type="PANGO_ANALYSIS_FLAG_IS_ELLIPSIS" version="1.36.7">
      <doc xml:space="preserve">This flag is used to mark runs that hold ellipsized text,
in an ellipsized layout.</doc>
      <type name="gint" c:type="gint"/>
    </constant>

As we don't define constants and use flags directly https://github.com/gtk-rs/pango/blob/master/src/analysis.rs#L38 IMHO we can just leave pango's fix and close this PR.