gccrs: Unify HIR::IfLetExprConseqIf{,Let} into HIR::IfLetExprConseqElse

gccrs: Unify HIR::IfLetExprConseqIf{,Let} into HIR::IfLetExprConseqElse

This should allow for 'if let' expressions to be lowered more easily.

gcc/rust/ChangeLog:

	* backend/rust-compile-block.h
	(CompileConditionalBlocks::visit): Remove IfLetExprConseqIf{,Let} visitors.
	(CompileExprWithBlock::visit): Remove IfLetExprConseqIf{,Let} visitors.
	* backend/rust-compile-expr.h
	(CompileExpr::visit): Remove IfLetExprConseqIf{,Let} visitors.
	* checks/errors/rust-unsafe-checker.cc
	(UnsafeChecker::visit): Remove IfLetExprConseqIf{,Let} visitors.
	* checks/errors/rust-unsafe-checker.h
	(UnsafeChecker::visit): Remove IfLetExprConseqIf{,Let} visitors.
	* checks/errors/rust-const-checker.cc
	(ConstChecker::visit): Remove IfLetExprConseqIf{,Let} visitors.
	* checks/errors/rust-const-checker.h
	(ConstChecker::visit): Remove IfLetExprConseqIf{,Let} visitors.
	* checks/errors/privacy/rust-privacy-reporter.cc
	(PrivacyReporter::visit): Remove IfLetExprConseqIf{,Let} visitors.
	* checks/errors/privacy/rust-privacy-reporter.h
	(PrivacyReporter::visit): Remove IfLetExprConseqIf{,Let} visitors.
	* hir/tree/rust-hir-expr.h
	(class IfLetExprConseqElse): Make else_block ExprWithBlock.
	(class IfLetExprConseqIf): Remove.
	(class IfLetExprConseqIfLet): Remove.
	* hir/tree/rust-hir-full-decls.h
	(class IfLetExprConseqIf): Remove.
	(class IfLetExprConseqIfLet): Remove.
	* hir/tree/rust-hir.cc
	(IfLetExprConseqElse::as_string): Adjust output.
	(IfLetExprConseqIf::as_string): Remove.
	(IfLetExprConseqIfLet::as_string): Remove.
	(IfLetExprConseqIf::accept_vis): Remove.
	(IfLetExprConseqIfLet::accept_vis): Remove.
	* hir/tree/rust-hir-visitor.h
	(HIRFullVisitor::visit): Remove IfLetExprConseqIf{,Let} visitors.
	(HIRFullVisitorBase::visit): Remove IfLetExprConseqIf{,Let} visitors.
	(HIRExpressionVisitor::visit): Remove IfLetExprConseqIf{,Let} visitors.
	* hir/rust-hir-dump.cc
	(Dump::visit): Remove IfLetExprConseqIf{,Let} visitors.
	* hir/rust-hir-dump.h
	(Dump::visit): Remove IfLetExprConseqIf{,Let} visitors.
	* typecheck/rust-hir-type-check-expr.h
	(TypeCheckExpr::visit): Remove IfLetExprConseqIf{,Let} visitors.

Signed-off-by: Owen Avery <powerboat9.gamer@gmail.com>