Update gdb.dwarf2/data-loc.exp

Tom de Vries pointed out that the series to handle
-fgnat-encodings=minimal regressed data-loc.exp:

https://sourceware.org/pipermail/gdb-patches/2020-November/173035.html

This was my oversight.  Looking at the test, it mimics what GNAT
emits.  The patch series in question changed the approach that gdb
takes to such arrays -- now they are transformed back into "old" style
structures.  (This is perhaps a step backward in a semantics sense,
but on the other hand it more accurately reflects the underlying
reality, and lets gdb continue to create objects of this type.)

This patch updates the test case, by adjusting the expected output.
It also removes the tests done in the C language, because they are now
incorrect, and because (IMO) they don't add much value.

gdb/testsuite/ChangeLog
2020-11-16  Tom Tromey  <tromey@adacore.com>

	* gdb.dwarf2/data-loc.exp: Update expected output.  Remove C
	tests.