configs/galileo_defconfig: remove legacy binutils version selection

Back when galileo_defconfig was added, an explicit binutils version was
used, because only binutils >= 2.25 had support for the
-momit-lock-prefix option, necessary to workaround a CPU issue.

Support for binutils 2.25 has now been removed from Buildroot, and
therefore the option no longer exists, causing a build failure. The
oldest binutils version that can be selected in Buildroot is binutils
2.26, which has support for -momit-lock-prefix. Therefore, we simply
remove the explicit binutils version selection.

Fixes:

  https://gitlab.com/buildroot.org/buildroot/builds/15762201



Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>