CtsNetTestCasesLatestSdk was originally used for MTS to prevent
installation issues with CUR_DEVELOPMENT target SDK modules (as is the
case for CtsNetTestCases) not installing on released devices.

However setting the min_sdk to a given value should be enough for that
purpose. While there may have been other blockers requiring separation
of CtsNetTestCases and CtsNetTestCasesLatestSdk at the time (in the Q/R
timeframe), more recent modules like CtsAdServicesDeviceTestCases seem
to be using CUR_DEVELOPMENT target SDK in MTS just fine.

Not specifying a target SDK means that the branch default will be used,
depending on the release configuration. So for example trunk_staging
would typically be CUR_DEVELOPMENT=10000, and "next" may use the SDK
version of that release.
This makes sense as a test suite targeting CUR_DEVELOPMENT is necessary
to verify a development build, while a production "next" configuration
should generally use the latest released SDK. But in any case, for
CtsNetTestCases purposes, this would cause the exercised connectivity
APIs to use their latest non-compatibility behavior, which is what
tests expect.

Considering this, add CtsNetTestCases to MTS, so that
CtsNetTestCasesLatestSdk can be removed. This will allow having one test
suite for both CTS and MTS, which in turns allows marking
CtsNetTestCases as MCTS, so that the version of the test to run is
autodetected based on installed modules.

Note this change also removes the unnecessary "platform_api" statement
and comment as this is already handled in
framework-connectivity-test-defaults.

Bug: 317913702
Test: m, aapt dump badging, verify (min)sdkVersion=30, targetSdk=10000
Change-Id: I2267e5c9219f059872928cc681547c3bd5fbc394