Documentation: Drop install directive for Doxyfile

Building the documentation reports warnings,

WARNING: Project targetting '>= 0.40' but tried to use feature introduced in '0.50.0': install arg in configure_file
WARNING: Project specifies a minimum meson_version '>= 0.40' but uses features which were added in newer versions:
 * 0.50.0: {'install arg in configure_file'}

Due to the usage of the directive configure_file { install: false } in
Documentation/meason.build which is introduced in meson 0.50. As we do
not wish to install the Doxyfile no install_dir is set so there is no
need to explicitly state that it should not be installed. Silence the
warning by dropping the install directive.

Fixes: 53c4d4c34f ("Documentation: Generate source code documentation using Doxygen")
Signed-off-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

Documentation/meson.build

@@ -14,8 +14,7 @@ if doxygen.found()
 
     doxyfile = configure_file(input: 'Doxyfile.in',
                               output: 'Doxyfile',
-                              configuration: cdata,
+                              configuration: cdata)
-                              install: false)
 
     custom_target('doxygen',
                   input: [