plugins/elements/gsttypefindelement.c: Deprecate "maximum" property (not only was it only taken into account for type...

Original commit message from CVS:
* plugins/elements/gsttypefindelement.c:
(gst_type_find_element_class_init),
(gst_type_find_element_set_property),
(gst_type_find_element_get_property):
Deprecate "maximum" property (not only was it only taken into
account for typefinding in push-mode anyway, it also was never
actually possible to set it in the first place because the
property was registered with the numeric property ID for the
"minimum" property). Register "maximum" property correctly,
for the sake of future copy'n'pasters. Remove some cruft
from property get/set functions.