gdb/dwarf: remove unnecessary check in read_{rng,loc}list_index

gdb/dwarf: remove unnecessary check in read_{rng,loc}list_index

In read_rnglist_index and read_loclist_index, we check that both the
start and end of the offset that we read from the offset table are
within the section.  I think it's unecessary to do both: if the end of
the offset is within the section, then surely the start of the offset is
within it.

Remove the check for the start of the offset in both functions.

gdb/ChangeLog:

	* dwarf2/read.c (read_loclist_index): Remove bound check for
	start of offset.
	(read_rnglist_index): Likewise.

Change-Id: I7b57ddf4f8a8a28971738f0e3f3af62108f9e19a