tests: Disable valgrind for run-large-elf-file and run-compress-test

tests: Disable valgrind for run-large-elf-file and run-compress-test

Both run-compress-test and run-large-elf-file create really big
files. Processing these under valgrind take a very long time. To
encourage more testing under valgrind memcheck or helgrind disable
valgrind for these two test so people don't have to wait 10 minutes
for make check results.

	* tests/run-compress-test.sh: Unset VALGRIND_CMD.
	* tests/run-large-elf-file.sh: Likewise.

Signed-off-by: Mark Wielaard <mark@klomp.org>