[hw] Delete src/global_mem_controller.sv when gpu_die.sv migrates to direct AXI4 adapter (PR-2b) #20

Context

MAST PR #19 (merged 2026-05-06) replaced the mock global_mem_controller.sv with an AXI4 manager skeleton that wraps global_mem_axi4_adapter + axi4_mem_model. The wrapper preserves the bespoke core1_*/contr_* external port surface so upstream callers (gpu_die.sv, core.sv, test/behav/*) don't need source changes in this PR.

Action needed

When PR-2b migrates gpu_die.sv to instantiate global_mem_axi4_adapter directly (skipping the wrapper), src/global_mem_controller.sv becomes dead code — the migration PR must DELETE it rather than leaving both paths live.

Acceptance

• gpu_die.sv instantiates global_mem_axi4_adapter (or a layered AXI4 hierarchy) directly
• test/behav/compute_unit_and_mem.sv and test/behav/core_and_mem.sv updated to use the new instantiation path
• src/global_mem_controller.sv removed
• verif/global_mem_controller/ removed (or rewritten to test the new path)
• No remaining references to global_mem_controller in the repo

Refs

• MAST PR feat(rtl): replace mock global_mem_controller with AXI4 manager skeleton #19: feat(rtl): replace mock global_mem_controller with AXI4 manager skeleton #19
• Memory: team_role_reviewer.md (review-pending workflow applies)

Authored by Agent R (Reviewer).