IMPALA-14985: Cleanup tests with unused 'vector' in EE tests

Having 'vector' argument leads to running a test as parametrized,
so running it with multiple parameter vectors. These parameters
don't affect how queries run unless passed to functions like
run_test_case() explicitly.

Note that unused 'vector's can give the false impression of
affecting the query options of queries run by default clients
as query option CLIENT_IDENTIFIER is actually modifed based
on the parameter vector using pytest hook pytest_runtest_logstart
and connections' clear_configuration and create_connection functions.

One example (TestIOMetrics) was found where the intention was to
pass num_nodes=1 but this didn't happen.

A test bug found during this change is that there were test classes
where "skip if not exhaustive" logic was implemented within
add_test_dimensions(), but this didn't affect non-parametrized
tests that were still run in core builds. This is fixed by
checking exploration strategy elsewhere.

The change also cleans up add_test_dimensions() functions which
are not used as the test class has no test function with
'vector' parameter.

Testing:
- passed exhaustive tests

Generated by: copilot + Claude Sonnet 4.6

Change-Id: I8e2a8fe333e33a906178a0821eb554890be26132
Reviewed-on: http://gerrit.cloudera.org:8080/24296
Reviewed-by: Noemi Pap-Takacs <npaptakacs@cloudera.com>
Tested-by: Csaba Ringhofer <csringhofer@cloudera.com>