[API-702] v5 SQL: Remove unused load balancer methods

[mdumandag]

These methods were specially added for 4.2 SQL, but they are unused
in v5. Hence, we are removing the unused methods and reverting the
changes we made around the load balancer implementations and tests.

Note that, it is perfectly safe to remove these methods in Python.
If there were users that implemented these methods, they can use
their code without changing anything.

[codecov-commenter]

Codecov Report

Merging #458 (1055116) into master (da647b8) will decrease coverage by 0.31%.
The diff coverage is 86.90%.

@@            Coverage Diff             @@
##           master     #458      +/-   ##
==========================================
- Coverage   94.51%   94.19%   -0.32%     
==========================================
  Files         345      345              
  Lines       17547    17563      +16     
==========================================
- Hits        16584    16543      -41     
- Misses        963     1020      +57     

Impacted Files	Coverage Δ
hazelcast/sql.py	96.83% <72.72%> (-0.61%)	⬇️
hazelcast/util.py	83.90% <82.05%> (-0.71%)	⬇️
hazelcast/connection.py	90.81% <96.42%> (-1.70%)	⬇️
hazelcast/__init__.py	60.00% <100.00%> (ø)
hazelcast/protocol/builtin.py	94.45% <100.00%> (-0.13%)	⬇️
...otocol/codec/client_authentication_custom_codec.py	50.00% <0.00%> (-23.81%)	⬇️
hazelcast/reactor.py	79.56% <0.00%> (-7.55%)	⬇️
hazelcast/proxy/base.py	97.40% <0.00%> (-0.65%)	⬇️
hazelcast/statistics.py	88.02% <0.00%> (-0.60%)	⬇️
... and 1 more

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