gdb.base/break-on-linker-gcd-function.exp: Remove unused variable

gdb.base/break-on-linker-gcd-function.exp: Remove unused variable

Commit:

 commit 4d142eaa28c64565b58fcdb5a83377ec9b778cb1
 Author:     Jan Kratochvil <jan.kratochvil@redhat.com>
 AuthorDate: Tue Jul 2 20:06:12 2013 +0000

     gdb/testsuite/
	     * gdb.base/break-on-linker-gcd-function.exp: Replace
	     prepare_for_testing by build_executable_from_specs and clean_restart.
 ...

did:

 set additional_flags {-ffunction-sections -Wl,--gc-sections}
 -if {[prepare_for_testing $testfile.exp $testfile $srcfile \
 -        [list debug c++ additional_flags=$additional_flags]]} {
 +if {[build_executable_from_specs $testfile.exp $testfile \
 +       {c++ additional_flags=-Wl,--gc-sections} \
 +       $srcfile {debug c++ additional_flags=-ffunction-sections}]} {

and that left the additional_flags variable behind.  Remove it.

gdb/testsuite/ChangeLog:

	* gdb.base/break-on-linker-gcd-function.exp: Remove unused
	'additional_flags' variable.