d: Remove visibility and lookup deprecation

d: Remove visibility and lookup deprecation

The deprecation phase for access checks is finished.

The `-ftransition=import` and `-ftransition=checkimports` switches no
longer have an effect and are now removed.  Symbols that are not visible
in a particular scope will no longer be found by the compiler.

Reviewed-on: https://github.com/dlang/dmd/pull/12124

gcc/d/ChangeLog:

	* dmd/MERGE: Merge upstream dmd 2d3d13748.
	* d-lang.cc (d_handle_option): Remove OPT_ftransition_checkimports and
	OPT_ftransition_import.
	* gdc.texi (Warnings): Remove documentation for -ftransition=import
	and -ftransition=checkimports.
	* lang.opt (ftransition=checkimports): Remove.
	(ftransition=import): Remove.