gccrs: libproc_macro: Remove has_suffix attribute

This variable was redundant with the empty string representation and
may have lead to desync between both.

libgrust/ChangeLog:

	* libproc_macro/literal.h: Remove has_suffix member
	attribute from Literal.
	* libproc_macro/literal.cc: Update constructors.
	* libproc_macro/rust/bridge/literal.rs: Remove
	has_suffix attribute from Literal.

Signed-off-by: Pierre-Emmanuel Patry <pierre-emmanuel.patry@embecosm.com>