systemc: Delete extra code from src/systemc/tlm_bridge.

systemc: Delete extra code from src/systemc/tlm_bridge.

Much of the code in src/systemc/tlm_bridge has been absorbed into the
TLM/gem5 bridge SimObjects and is no longer needed and redundant with
the original version in util/.

Change-Id: I0fa7af67649987cf9f6fc5cd4783002dde2242ac
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/17233
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>