Remove unnecessary section headers in ODE documentation

Consolidate 'Initial Value Problems' and 'Continuous Dynamical Systems' sections as they don't need to be separate.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: ChrisRackauckas

docs/src/manual/ode.md

@@ -35,13 +35,10 @@ Symbolics.SymbolicLinearODE
 Symbolics.symbolic_solve_ode
 ```
 
-### Initial Value Problems
-
 ```@docs
 Symbolics.solve_symbolic_IVP
 ```
 
-### Continuous Dynamical Systems
 ```@docs
 Symbolics.solve_linear_ode_system
 ```