modules: lvgl: Remove Kconfig symbols that dont exist

LV_Z_DISPLAY_DEV_NAME, LV_Z_HOR_RES_MAX, & LV_Z_VER_RES_MAX
Kconfig symbols don't exist anymore.  They got removed in
recent devicetree update of lvgl module.  So remove them from
modules/Kconfig.lvgl.

Signed-off-by: Kumar Gala <galak@kernel.org>