defconfig: Disable CONFIG_FORTIFY_SOURCE

This build option is broken for clang and upstream removed it in commit
9000f2a528c0 ("fortify: Explicitly disable Clang support") so we have to
also remove it for the gki defconfigs.

Fixes: 9000f2a528c0 ("fortify: Explicitly disable Clang support")
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: I8d4a1d38b736ee1fd4a6febfbab4d1a3c1c4d351