serial: remove drivers for espressif esp32

serial: remove drivers for espressif esp32

These drivers were added about 3 years ago, and depend on the
XTENSA_PLATFORM_ESP32 config option which has never existed,
so no device can actually use them.
They can only be compiled with COMPILE_TEST.

In a previous conversation [1], Greg suggested removing the
drivers, and Max, the original submitter of the drivers, agreed
due to a lack of foreseeable development.

Link: https://lore.kernel.org/all/20260308131412.1102749-1-julianbraha@gmail.com/
Signed-off-by: Julian Braha <julianbraha@gmail.com>
Link: https://patch.msgid.link/20260309122321.1528622-1-julianbraha@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>