gdbserver/linux-low: delete 'linux_target_ops' and 'the_low_target'

gdbserver/linux-low: delete 'linux_target_ops' and 'the_low_target'

All the linux target ops have been moved into linux_process_target
as methods.  The 'linux_target_ops' struct and its instantiations
are now obsolete.  Delete them.

gdbserver/ChangeLog:
2020-04-02  Tankut Baris Aktemur  <tankut.baris.aktemur@intel.com>

	* linux-low.h (struct linux_target_ops): Remove.
	(the_low_target): Remove.
	* linux-x86-low.cc (the_low_target): Remove.
	* linux-aarch64-low.cc (the_low_target): Ditto.
	* linux-arm-low.cc (the_low_target): Ditto.
	* linux-bfin-low.cc (the_low_target): Ditto.
	* linux-cris-low.cc (the_low_target): Ditto.
	* linux-crisv32-low.cc (the_low_target): Ditto.
	* linux-ia64-low.cc (the_low_target): Ditto.
	* linux-m32r-low.cc (the_low_target): Ditto.
	* linux-m68k-low.cc (the_low_target): Ditto.
	* linux-mips-low.cc (the_low_target): Ditto.
	* linux-nios2-low.cc (the_low_target): Ditto.
	* linux-ppc-low.cc (the_low_target): Ditto.
	* linux-riscv-low.cc (the_low_target): Ditto.
	* linux-s390-low.cc (the_low_target): Ditto.
	* linux-sh-low.cc (the_low_target): Ditto.
	* linux-sparc-low.cc (the_low_target): Ditto.
	* linux-tic6x-low.cc (the_low_target): Ditto.
	* linux-tile-low.cc (the_low_target): Ditto.
	* linux-xtensa-low.cc (the_low_target): Ditto.