chore: move plugins to access from model dir

Remove access and setup of plugins from public downloads area.
Assume all plugins are present with model binaries.

Currently with RevC model we are using the following plugins
 - ETMv4ExamplePlugin.so
 - GenericTrace.so
 - libete-plugin.so

A new RevC model package FVP_Base_RevC-2xAEMvA_11.26_11_Linux64.tgz
has been uploaded this package contains both the plugins in plugins
directory.

Change-Id: I0e0f2dd014b6cfa8b6bfa0556db15715814bd9b4
Signed-off-by: Govindraj Raja <govindraj.raja@arm.com>
(cherry picked from commit 7d80d9370e9001097c30a6518c35831fe6ae3a5b)
diff --git a/model/base-aemva-common.sh b/model/base-aemva-common.sh
index 018e576..0d502bb 100644
--- a/model/base-aemva-common.sh
+++ b/model/base-aemva-common.sh
@@ -292,8 +292,8 @@
 -C pci.tbu0_pre_smmu_logger.trace_debug=1
 -C pci.pci_smmuv3.mmu.all_error_messages_through_trace=1
 -C TRACE.GenericTrace.trace-sources=verbose_commentary,smmu_initial_transaction,smmu_final_transaction,*.pci.pci_smmuv3.mmu.*,*.pci.smmulogger.*,*.pci.tbu0_pre_smmu_logger.*,smmu_poison_tw_data
---plugin $warehouse/SysGen/PVModelLib/$model_version/$model_build/external/plugins/$model_flavour/GenericTrace.so
 -C cci550.force_on_from_start=1
+--plugin $generictrace_plugin_path
 EOF
 
 # If RME is implemented: