Plugin remap: fix plugin inheritance not being loaded

Before this change, the inheritance map would always be empty.
Note it is still incomplete.
Plugin remap: add optional debugging

Enable extra debugging messages with -Dmcpc.debugPluginRemap=true

The existing (non-debug) informational log messages remain present, but
can be disabled with -Dmcpc.debugPluginRemap=false (on by default)
Plugin remap: remove unnecessary stubs in ApplySrg

No longer required in recent versions of ASM, since ClassVisitor
is a class you extend instead of an interface you implement.