gdb: Remove an update of current_source_line and current_source_symtab

gdb: Remove an update of current_source_line and current_source_symtab

While reviewing some of the annotation code I noticed that
identify_source_line (in source.c) sets current_source_line,
current_source_symtab, and also calls clear_lines_listed_range.  This
seems a little strange, identify_source_line is really a wrapper
around annotate_source, and is only called when annotation_level is
greater than 0 (so annotations are turned on).

It seems weird (to me) that when annotations are on we update GDB's
idea of the "current" line/symtab, but when they are off we don't,
given that annotations are really about communicating GDB's state to a
user (GUI) and surely shouldn't be changing GDB's behaviour.

This commit removes from identify_source_line all of the setting of
current line/symtab and the call to clear_lines_listed_range, after
doing this GDB still passes all tests, so I don't believe these lines
were actually required.

With this code removed identify_source_line is only a wrapper around
annotate_source, so I moved identify_source_line to annotate.c and
renamed it to annotate_source_line.

gdb/ChangeLog:

	* annotate.c: Add 'source.h' and 'objfiles.h' includes.
	(annotate_source): Make static.
	(annotate_source_line): Moved from source.c and renamed from
	identify_source_line.  Update the return type.
	* annotate.h (annotate_source): Delete declaration.
	(annotate_source_line): Declaration moved from source.h, and
	renamed from identify_source_line.  Return type updated.
	* source.c (identify_source_line): Moved to annotate.c and renamed
	to annotate_source_line.
	(info_line_command): Remove check of annotation_level.
	* source.h (identify_source_line): Move declaration to annotate.h
	and rename to annotate_source_line.
	* stack.c: Add 'annotate.h' include.
	(print_frame_info): Remove check of annotation_level before
	calling annotate_source_line.