c++: remove LAMBDA_EXPR_MUTABLE_P
In review of the deducing 'this' patch it came up that LAMBDA_EXPR_MUTABLE_P
doesn't make sense for a lambda with an explicit object parameter. And it
was never necessary, so let's remove it.
gcc/cp/ChangeLog:
* cp-tree.h (LAMBDA_EXPR_MUTABLE_P): Remove.
* cp-tree.def: Remove documentation.
* lambda.cc (build_lambda_expr): Remove reference.
* parser.cc (cp_parser_lambda_declarator_opt): Likewise.
* pt.cc (tsubst_lambda_expr): Likewise.
* ptree.cc (cxx_print_lambda_node): Likewise.
* semantics.cc (capture_decltype): Get the object quals
from the object instead.