[kernel] Removes old impact pragma (now replaced by an ACSL extension).

src/kernel_internals/parsing/logic_parser.mly

src/kernel_services/analysis/logic_deps.ml

src/kernel_services/ast_data/cil_types.ml

src/kernel_services/ast_printing/cil_printer.ml

src/kernel_services/ast_printing/cil_types_debug.ml

src/kernel_services/ast_printing/cil_types_debug.mli

src/kernel_services/ast_printing/logic_print.ml

src/kernel_services/ast_queries/ast_diff.ml

src/kernel_services/ast_queries/cil.ml

src/kernel_services/ast_queries/cil.mli

src/kernel_services/ast_queries/logic_typing.ml

src/kernel_services/ast_queries/logic_utils.ml

src/kernel_services/ast_queries/logic_utils.mli

src/kernel_services/parsetree/logic_ptree.ml

src/plugins/impact/register.ml

src/plugins/metrics/metrics_pivot.ml