Removed unused references to CONFIG_SERIALx

After creating CONS_INDEX and migrating a bunch of boards to it,
there are a bunch of defined references to CONFIG_SERIALx which
are not referenced in any C code or #ifdef, so they can now be
removed

Signed-off-by: Adam Ford <aford173@gmail.com>
diff --git a/configs/am43xx_evm_qspiboot_defconfig b/configs/am43xx_evm_qspiboot_defconfig
index df2ea1e..985a475 100644
--- a/configs/am43xx_evm_qspiboot_defconfig
+++ b/configs/am43xx_evm_qspiboot_defconfig
@@ -5,7 +5,7 @@
 CONFIG_AM43XX=y
 CONFIG_DEFAULT_DEVICE_TREE="am437x-sk-evm"
 CONFIG_DISTRO_DEFAULTS=y
-CONFIG_SYS_EXTRA_OPTIONS="SERIAL1,CONS_INDEX=1,QSPI,QSPI_BOOT"
+CONFIG_SYS_EXTRA_OPTIONS="CONS_INDEX=1,QSPI,QSPI_BOOT"
 CONFIG_QSPI_BOOT=y
 # CONFIG_USE_BOOTCOMMAND is not set
 CONFIG_SYS_CONSOLE_INFO_QUIET=y