Removing SQLv1 API support + small SQL model fixes

[Temikus]

Support for First Generation instances ended January 30, 2020 and you no longer can create First Generation instances.

See: https://cloud.google.com/sql/docs/mysql/upgrade-2nd-gen

[Temikus]

@icco I'm not going to break compatibility, but I am planning to remove the CI, tests and any first-tier exclusive methods as they're going to be unusable.

You reckon this should be a minor or a major version release?

[icco]

Minor I think is reasonable

[codecov]

Codecov Report

Merging #493 into master will increase coverage by 1.06%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #493      +/-   ##
==========================================
+ Coverage   87.94%   89.01%   +1.06%     
==========================================
  Files         340      340              
  Lines        5659     5661       +2     
==========================================
+ Hits         4977     5039      +62     
+ Misses        682      622      -60

Impacted Files	Coverage Δ
lib/fog/google/models/sql/ssl_cert.rb	89.18% <100%> (+34.9%)	⬆️
lib/fog/google/models/sql/instance.rb	79.5% <0%> (+10.65%)	⬆️
lib/fog/google/requests/sql/list_users.rb	100% <0%> (+12.5%)	⬆️
lib/fog/google/requests/sql/delete_user.rb	100% <0%> (+12.5%)	⬆️
...g/google/requests/sql/reset_instance_ssl_config.rb	100% <0%> (+12.5%)	⬆️
lib/fog/google/requests/sql/insert_ssl_cert.rb	100% <0%> (+12.5%)	⬆️
lib/fog/google/requests/sql/delete_ssl_cert.rb	100% <0%> (+12.5%)	⬆️
lib/fog/google/requests/sql/get_ssl_cert.rb	100% <0%> (+12.5%)	⬆️
lib/fog/google/requests/sql/list_ssl_certs.rb	100% <0%> (+12.5%)	⬆️
lib/fog/google/requests/sql/insert_user.rb	100% <0%> (+12.5%)	⬆️
... and 5 more

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