fix: use rdkit API to remove implicit hydrogens (#2278)

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-->

## Summary by CodeRabbit

- **New Features**
- Enhanced SMILES conversion process with improved implicit hydrogen
handling for atoms.
  
- **Bug Fixes**
- Removed outdated method that previously handled SMILES conversion,
streamlining the conversion process.

- **Tests**
- Removed a test related to the now-removed SMILES handling method,
reflecting updates in testing strategy.

- **Chores**
- Minor formatting adjustments and removal of unused imports for cleaner
code.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

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Signed-off-by: Jinzhe Zeng <[email protected]>

reacnetgenerator/_path.py

@@ -264,6 +264,10 @@ def convertSMILES(self, atoms, bonds):
             d[number] = m.AddAtom(Chem.Atom(name))
         for atom1, atom2, level in bonds:
             m.AddBond(d[atom1], d[atom2], Chem.BondType(level))
+        # https://github.com/rdkit/rdkit/discussions/6613#discussioncomment-6688021
+        for a in m.GetAtoms():  # type:ignore
+            a.SetNoImplicit(True)
+            a.UpdatePropertyCache()
         name = Chem.MolToSmiles(m)
         return self._re(name)