[common.configtree] remove guard of local header

Those can always be included!
[common.tuple] update include guard
[fem.customprojection] update include guards
[grid.entity] do not guard geometry include with HAVE_DUNE_GRID
[grid.search] guard complete header with HAVE_DUNE_GRID
[grid.structuredgridfactory] do not guard local include
[grid.walk] update include guard
[la.container] remove obsolete include
[ŧest.common_string] do not guard include of local header

Those can always be included!
[ŧest.functions_combined] remove DUNE_STUFF_TEST_MAIN_CATCH_EXCEPTIONS
[test.functions_constant] reenable HAVE_DUNE_GRID guard
remove {disable,reenable}_warning guards, closes #20