Remove struct keyword from section_addr_info

Remove struct keyword from section_addr_info

Buildbot pointed out a failiure in windows-nat.c:

../../binutils-gdb/gdb/windows-nat.c:582:10: error: using typedef-name 'section_addr_info' after 'struct'
   struct section_addr_info *addrs;
          ^~~~~~~~~~~~~~~~~
In file included from ../../binutils-gdb/gdb/windows-nat.c:49:0:
../../binutils-gdb/gdb/symfile.h:75:37: note: 'section_addr_info' has a previous declaration here
 typedef std::vector<other_sections> section_addr_info;
                                     ^~~~~~~~~~~~~~~~~

A recursive grep of the sources for "struct section_addr_info" reveals one
additional reference in a comment.  In both cases, this patch simply removes
the struct keyword.

gdb/ChangeLog:

	* symfile.c (place_section): Remove "struct" from section_addr_info
	in comment.
	* windows-nat.c (struct safe_symbol_file_add_args) <addrs>: Remove
	"struct" keyword from section_addr_info.