Remove install_desktop_file

After the previous commits, install_desktop_file is now reduced to the
same functionality as install_data, so use this function.

install.sh

@@ -73,11 +73,6 @@ function install_if()
     return 0
 }
 
-function install_desktop_file()
-{
-    install_if "$1" "$2" $INSTALL_DATA
-}
-
 function install_exec()
 {
     install_if "$1" "$2" $INSTALL_PROGRAM
@@ -195,14 +190,12 @@ install_exec checktrust/lightdm-show-trust-warning        "$DESTDIR$usr_exec_pre
 install_symlink /node/issue.d/notrust.issue               "$DESTDIR$sysconfdir/issue.d/notrust.issue"
 install_data checktrust/getty-checktrust.service          "$DESTDIR$systemdunitdir/getty-checktrust.service"
 install_exec checktrust/getty-checktrust                  "$DESTDIR$usr_exec_prefix/libexec/getty-checktrust"
-install_desktop_file desktop-files/org.inkscape.Inkscape.desktop \
-                                                          "$DESTDIR$desktopdir/org.inkscape.Inkscape.desktop"
-install_desktop_file desktop-files/rstudio.desktop        "$DESTDIR$desktopdir/rstudio.desktop"
-install_desktop_file desktop-files/meld3.desktop          "$DESTDIR$desktopdir/meld3.desktop"
-install_desktop_file desktop-files/ugene.desktop          "$DESTDIR$desktopdir/ugene.desktop"
-install_desktop_file desktop-files/org.octave.Octave.desktop \
-                                                          "$DESTDIR$desktopdir/org.octave.Octave.desktop"
-install_desktop_file desktop-files/igv.desktop            "$DESTDIR$desktopdir/igv.desktop"
+install_data desktop-files/org.inkscape.Inkscape.desktop  "$DESTDIR$desktopdir/org.inkscape.Inkscape.desktop"
+install_data desktop-files/rstudio.desktop                "$DESTDIR$desktopdir/rstudio.desktop"
+install_data desktop-files/meld3.desktop                  "$DESTDIR$desktopdir/meld3.desktop"
+install_data desktop-files/ugene.desktop                  "$DESTDIR$desktopdir/ugene.desktop"
+install_data desktop-files/org.octave.Octave.desktop      "$DESTDIR$desktopdir/org.octave.Octave.desktop"
+install_data desktop-files/igv.desktop                    "$DESTDIR$desktopdir/igv.desktop"
 
 postinstall
 exit