Fix duplicated <remarks> open tag in TryGetGlyphMetrics doc

The vertical-metrics doc update left two consecutive `<remarks>` opening
lines with a single closing tag, producing malformed XML (CS1570). That
is only a warning under Debug but a hard error in Release, where
Directory.Build.props sets TreatWarningsAsErrors=true — so CI (warnings
as errors) would fail this branch. Drop the duplicate line.

Author: Gillibald

src/Avalonia.Base/Media/GlyphTypeface.cs

@@ -704,7 +704,6 @@ public bool TryGetVerticalGlyphAdvances(ReadOnlySpan<ushort> glyphIds, Span<usho
         /// Attempts to retrieve the metrics for the specified glyph.
         /// </summary>
         /// <remarks>This method returns metrics only if horizontal or vertical metrics are available for
-        /// <remarks>This method returns metrics only if horizontal or vertical metrics are available for
         /// the specified glyph. If neither is available, the method returns false and the output parameter is set to
         /// its default value.</remarks>
         /// <param name="glyph">The identifier of the glyph for which to obtain metrics.</param>