Remove redundant rebalancing of P4estMesh

Once https://github.com/cburstedde/p4est/issues/112 is fixed, we should remove redundant calls to `p4est_balance` like in code like this:
https://github.com/trixi-framework/Trixi.jl/blob/dd5e28e03cffcc391a4ca9536a498613c0c6ecd4/src/solvers/dg_p4est/dg.jl#L7-L10

First check whether p4est issue 112 is fixed, then inspect the referenced lines in src/solvers/dg_p4est/dg.jl around p4est_balance. Remove the redundant rebalancing calls once the dependency is resolved, and verify the existing Trixi.jl tests or simulations still run correctly.

Written by the indexing model from the issue text.