Remove unused colorIndexed member.

As all the indexed colors will be converted to rgb in the library when
reads an existing .xlsx file.

When write a .xlsx file, we never write indexed color.

src/xlsx/xlsxformat.cpp

@@ -42,7 +42,6 @@ FormatPrivate::FormatPrivate(Format *p) :
     dxf_indexValid = false;
 
     theme = 0;
-    color_indexed = 0;
 }
 
 /*!
@@ -983,10 +982,4 @@ int Format::theme() const
     return d->theme;
 }
 
-int Format::colorIndexed() const
-{
-    Q_D(const Format);
-    return d->color_indexed;
-}
-
 QT_END_NAMESPACE_XLSX

src/xlsx/xlsxformat.h

@@ -253,7 +253,6 @@ private:
     void setDxfIndex(int index);
 
     int theme() const;
-    int colorIndexed() const;
 
     FormatPrivate * const d_ptr;
 };

src/xlsx/xlsxformat_p.h

@@ -266,7 +266,6 @@ public:
     bool dxf_indexValid;
 
     int theme;
-    int color_indexed;
 
     Format *q_ptr;
 };