Follow-up the PR #3631(Encapsulate Stepper, Planner, Endstops in singleton classes)

plan_bed_level_matrix -> planner.bed_level_matrix in multi extruders section of Marlin_main.cpp
It probably fix the Issue #3658(plan_bed_level_matrix not declarate).

movesplanned() -> planner.movesplanned() in ADVANCED_OK section of Marlin_main.cpp
It fix compilation error when ADVANCED_OK is enabled