remove examples for dnlp

[Transurgeon]

This PR removes examples from the DNLP repo.
They should be moved to the dnlp-examples repository.
I did a similar PR for cvxpy master to remove examples there. See this. So I wanted to cleanup the diff for DNLP as well.

[github-actions]

Benchmarks that have stayed the same:

   before           after         ratio
 [496bbf35]       [70552e83]
     14.4±0ms         14.8±0ms     1.03  simple_QP_benchmarks.ParametrizedQPBenchmark.time_compile_problem
      5.05±0s          5.15±0s     1.02  svm_l1_regularization.SVMWithL1Regularization.time_compile_problem
      1.65±0s          1.68±0s     1.02  tv_inpainting.TvInpainting.time_compile_problem
      165±0ms          167±0ms     1.01  high_dim_convex_plasticity.ConvexPlasticity.time_compile_problem
      231±0ms          234±0ms     1.01  gini_portfolio.Murray.time_compile_problem
      295±0ms          298±0ms     1.01  slow_pruning_1668_benchmark.SlowPruningBenchmark.time_compile_problem
     14.4±0ms         14.5±0ms     1.01  simple_LP_benchmarks.SimpleFullyParametrizedLPBenchmark.time_compile_problem
      1.36±0s          1.37±0s     1.01  matrix_stuffing.ParamConeMatrixStuffing.time_compile_problem
      12.9±0s          13.0±0s     1.01  finance.CVaRBenchmark.time_compile_problem
      1.84±0s          1.86±0s     1.01  simple_QP_benchmarks.UnconstrainedQP.time_compile_problem
      672±0ms          674±0ms     1.00  matrix_stuffing.ConeMatrixStuffingBench.time_compile_problem
      1.06±0s          1.06±0s     1.00  finance.FactorCovarianceModel.time_compile_problem
      834±0ms          835±0ms     1.00  simple_QP_benchmarks.LeastSquares.time_compile_problem
      11.4±0s          11.4±0s     1.00  simple_LP_benchmarks.SimpleLPBenchmark.time_compile_problem
      4.96±0s          4.97±0s     1.00  optimal_advertising.OptimalAdvertising.time_compile_problem
      338±0ms          338±0ms     1.00  gini_portfolio.Yitzhaki.time_compile_problem
      939±0ms          939±0ms     1.00  simple_LP_benchmarks.SimpleScalarParametrizedLPBenchmark.time_compile_problem
      1.10±0s          1.10±0s     1.00  gini_portfolio.Cajas.time_compile_problem
      22.2±0s          22.2±0s     1.00  sdp_segfault_1132_benchmark.SDPSegfault1132Benchmark.time_compile_problem
      281±0ms          280±0ms     1.00  matrix_stuffing.ParamSmallMatrixStuffing.time_compile_problem
      257±0ms          256±0ms     1.00  simple_QP_benchmarks.SimpleQPBenchmark.time_compile_problem
      4.55±0s          4.53±0s     0.99  huber_regression.HuberRegression.time_compile_problem
     39.6±0ms         38.8±0ms     0.98  matrix_stuffing.SmallMatrixStuffing.time_compile_problem
      2.94±0s          2.86±0s     0.97  quantum_hilbert_matrix.QuantumHilbertMatrix.time_compile_problem
      529±0ms          514±0ms     0.97  semidefinite_programming.SemidefiniteProgramming.time_compile_problem

[dance858]

Cheers!