Remove Python 2.4 and 2.5 support

This removes all the remainings spots I could find that work around
issues in Python 2.4 and 2.5.

I don't have a good way to test that Python 2.6 still works.

Tested by the buildbot.

gdb/ChangeLog
2019-02-27  Tom Tromey  <tromey@adacore.com>

	* config.in, configure: Rebuild.
	* configure.ac (HAVE_LIBPYTHON2_4, HAVE_LIBPYTHON2_5): Never
	define.
	* python/py-value.c: Remove Python 2.4 workaround.
	* python/py-utils.c (gdb_pymodule_addobject): Remove Python 2.4
	workaround.
	* python/py-type.c (convert_field, gdbpy_initialize_types): Remove
	Python 2.4 workaround.
	* python/python-internal.h: Remove Python 2.4 comment.
	(Py_ssize_t): Don't define.
	(PyVarObject_HEAD_INIT, Py_TYPE): Don't define.
	(gdb_Py_DECREF): Remove Python 2.4 workaround.
	(gdb_PyObject_GetAttrString, PyObject_GetAttrString): Remove.
	(gdb_PyObject_HasAttrString, PyObject_HasAttrString): Remove.
	* python/python.c (do_start_initialization): Remove Python 2.4
	workaround.
	* python/py-prettyprint.c (class dummy_python_frame): Remove.
	(print_children): Remove Python 2.4 workaround.
	* python/py-inferior.c (buffer_procs): Remove Python 2.4
	workaround.
	(CHARBUFFERPROC_NAME): Remove.
	* python/py-breakpoint.c (gdbpy_initialize_breakpoints): Remove
	Python 2.4 workaround.

gdb/testsuite/ChangeLog
2019-02-27  Tom Tromey  <tromey@adacore.com>

	* lib/gdb.exp (skip_python_tests_prompt): Don't check for Python
	2.4.
	* gdb.python/py-finish-breakpoint.exp: Remove Python 2.4
	workaround.

gdb/ChangeLog
2019-02-27  Tom Tromey  <tromey@adacore.com>

	* config.in, configure: Rebuild.
	* configure.ac (HAVE_LIBPYTHON2_4, HAVE_LIBPYTHON2_5): Never
	define.
	* python/py-value.c: Remove Python 2.4 workaround.
	* python/py-utils.c (gdb_pymodule_addobject): Remove Python 2.4
	workaround.
	* python/py-type.c (convert_field, gdbpy_initialize_types): Remove
	Python 2.4 workaround.
	* python/python-internal.h: Remove Python 2.4 comment.
	(Py_ssize_t): Don't define.
	(PyVarObject_HEAD_INIT, Py_TYPE): Don't define.
	(gdb_Py_DECREF): Remove Python 2.4 workaround.
	(gdb_PyObject_GetAttrString, PyObject_GetAttrString): Remove.
	(gdb_PyObject_HasAttrString, PyObject_HasAttrString): Remove.
	* python/python.c (do_start_initialization): Remove Python 2.4
	workaround.
	* python/py-prettyprint.c (class dummy_python_frame): Remove.
	(print_children): Remove Python 2.4 workaround.
	* python/py-inferior.c (buffer_procs): Remove Python 2.4
	workaround.
	(CHARBUFFERPROC_NAME): Remove.
	* python/py-breakpoint.c (gdbpy_initialize_breakpoints): Remove
	Python 2.4 workaround.