Slightly simplify minsym creation

Slightly simplify minsym creation

Only one caller of minimal_symbol_reader::record_with_info was using
the return value, so this patch simplifies this code by having it
return void and changing that caller to use record_full instead.

gdb/ChangeLog
2019-03-15  Tom Tromey  <tom@tromey.com>

	* minsyms.h (class minimal_symbol_reader) <record_with_info>:
	Don't return the symbol.
	* coffread.c (record_minimal_symbol): Use record_full.