Remove warning -Wshadow

[rbuj]

mate-screensaver-preferences.c:195:36: warning: declaration of 'theme_manager' shadows a global declaration [-Wshadow]
  195 | get_all_theme_ids (GSThemeManager *theme_manager)
      |                    ~~~~~~~~~~~~~~~~^~~~~~~~~~~~~
--
mate-screensaver-preferences.c:300:28: warning: declaration of 'job' shadows a global declaration [-Wshadow]
  300 | job_set_theme (GSJob      *job,
      |                ~~~~~~~~~~~~^~~
--
mate-screensaver-dialog.c:432:76: warning: declaration of 'verbose' shadows a global declaration [-Wshadow]
  432 | static gboolean privileged_initialization(int* argc, char** argv, gboolean verbose)
      |                                                                   ~~~~~~~~~^~~~~~~
--
mate-screensaver-dialog.c:474:93: warning: declaration of 'verbose' shadows a global declaration [-Wshadow]
  474 | static gboolean lock_initialization (int* argc, char** argv, char** nolock_reason, gboolean verbose)
      |                                                                                    ~~~~~~~~~^~~~~~~
--
floaters.c:839:36: warning: declaration of 'max_floater_count' shadows a global declaration [-Wshadow]
  839 |                   gint             max_floater_count,
      |                   ~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~
--
floaters.c:840:36: warning: declaration of 'should_do_rotations' shadows a global declaration [-Wshadow]
  840 |                   gboolean         should_do_rotations,
      |                   ~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~
--
floaters.c:841:36: warning: declaration of 'should_show_paths' shadows a global declaration [-Wshadow]
  841 |                   gboolean         should_show_paths)
      |                   ~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~