t1091/t3705: remove 'test-tool read-cache --table'

t1091/t3705: remove 'test-tool read-cache --table'

Now that 'git ls-files --sparse' exists, we can use it to verify the
state of a sparse index instead of 'test-tool read-cache table'. Replace
these usages within t1091-sparse-checkout-builtin.sh and
t3705-add-sparse-checkout.sh.

The important changes are due to the different output format. In t3705,
we need to use the '--stage' output to get a file mode and OID, but
it also includes a stage value and drops the object type. This leads
to some differences in how we handle looking for specific entries.

In t1091, the test focuses on enabling the sparse index, so we do not
need the --stage flag to demonstrate how the index changes, and instead
can use a diff.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>