Clean two_qubit_decompose code

[ShellyGarion]

Summary

In this PR we remove some unused code from the file qiskit/synthesis/two_qubit/two_qubit_decompose.py.
And moreover, the following Python functions now calls the relevant Rust functions:

• decompose_two_qubit_product_gate
• trace_to_fid
• Ud

Details and comments

[qiskit-bot]

One or more of the following people are relevant to this code:

• @Qiskit/terra-core
• @kevinhartman
• @levbishop
• @mtreinish

[coveralls]

Pull Request Test Coverage Report for Build 10806927953

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 57 of 58 (98.28%) changed or added relevant lines in 2 files are covered.
• 795 unchanged lines in 31 files lost coverage.
• Overall coverage decreased (-0.3%) to 88.859%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
qiskit/synthesis/two_qubit/two_qubit_decompose.py	2	3	66.67%

Files with Coverage Reduction	New Missed Lines	%
qiskit/quantum_info/operators/mixins/multiply.py	1	93.75%
qiskit/synthesis/one_qubit/one_qubit_decompose.py	1	70.67%
qiskit/quantum_info/operators/mixins/group.py	1	92.59%
qiskit/transpiler/passes/synthesis/unitary_synthesis.py	1	88.26%
crates/qasm2/src/expr.rs	1	94.02%
qiskit/quantum_info/operators/channel/quantum_channel.py	1	72.14%
qiskit/quantum_info/operators/mixins/adjoint.py	1	90.0%
qiskit/quantum_info/operators/mixins/linear.py	1	88.0%
crates/accelerate/src/synthesis/clifford/utils.rs	1	78.06%
qiskit/visualization/circuit/_utils.py	2	94.25%

Totals
Change from base Build 10721003464:	-0.3%
Covered Lines:	73114
Relevant Lines:	82281

---

💛 - Coveralls

[mtreinish]

This LGTM, thanks for doing this. I have two small nits inline but otherwise I think this is good to go.

[mtreinish]

This LGTM, just one inline question/suggestion otherwise I think this is good to go.

[mtreinish]

LGTM, thanks for updating.