gccrs: Remove monomorphization hack to setup possible associated types

gccrs: Remove monomorphization hack to setup possible associated types

During CallExpr argument type checking we may be calling a default
implementation of a trait function this will require any possible
associated types to be resolved and setup. This monomoprhization call does
this but it will premtivly do extra unification of types which will throw
off type checking later on. This fix is required for my work into type
bounds checking.

Fixes #1773

Signed-off-by: Philip Herron <herron.philip@googlemail.com>
gcc/rust/ChangeLog:

	* typecheck/rust-hir-trait-reference.h: change interface to return self
	* typecheck/rust-hir-trait-resolve.cc: likewise
	* typecheck/rust-hir-type-check-path.cc (TypeCheckExpr::resolve_segments): likewise
	* typecheck/rust-tyty-call.cc (TypeCheckCallExpr::visit): remove monomorphization hack

gcc/testsuite/ChangeLog:

	* rust/compile/issue-1773.rs: New test.