Remove dead globals g_repl_owner and g_loading_scope_name

[python-processing-unit]

Problem

src/extensions.c maintains two globals that are written but never read:

• g_repl_owner (line 65): heap-allocated, stored, freed at shutdown (line 955), but never consulted.
• g_loading_scope_name (line 44): assigned at line 698, reset at lines 702 and 931, but never read.

Fix

Delete both variables and their assignment/reset sites.

Reported by Kilo Code (automated audit tool), not a human reviewer.