Fix spelling in the deep profiler.

Fix some other issues as well that I found while fixing the spelling.

mdbcomp/feedback.automatic_parallelism.m:
deep_profiler/autopar_find_best_par.m:
deep_profiler/mdprof_create_feedback.m:
    Rename the best_par_algorithm type to alg_for_finding_best_par,
    since the old name was misleading. Perform the same rename for
    another type based on it, and the option specifying it.

    Remove the functor estimate_speedup_by_num_vars, since it hasn't
    been used by anything in a long time, and won't in the future.

deep_profiler/autopar_calc_overlap.m:
deep_profiler/autopar_costs.m:
deep_profiler/autopar_reports.m:
deep_profiler/autopar_search_callgraph.m:
deep_profiler/autopar_search_goals.m:
deep_profiler/coverage.m:
deep_profiler/create_report.m:
deep_profiler/dump.m:
deep_profiler/mdprof_report_feedback.m:
deep_profiler/measurement_units.m:
deep_profiler/measurements.m:
deep_profiler/message.m:
deep_profiler/query.m:
deep_profiler/recursion_patterns.m:
deep_profiler/report.m:
deep_profiler/startup.m:
deep_profiler/var_use_analysis.m:
mdbcomp/mdbcomp.goal_path.m:
mdbcomp/program_representation.m:
    Conform to the above. Fix spelling errors. In some places, improve
    comments and/or variable names.