STM32: disable CONSOLE_* checks in for serial if no console available

[chrJost]

Summary of changes

This PR removes checks in serial_init in case no console is available. This fixes problems when the CONSOLE_TX and CONSOLE_RX pins are defined, but the console itself is disabled.

This was checked on a STM32L552 chip, but can affect all STM32 derivates.

Impact of changes

For the default use cases this patch should not have any impact.

Migration actions required

Documentation

None.

Pull request type

[X] Patch update (Bug fix / Target update / Docs update / Test update / Refactor)
[] Feature update (New feature / Functionality change / New API)
[] Major update (Breaking change E.g. Return code change / API behaviour change)

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Test results

[X] No Tests required for this change (E.g docs only update)
[] Covered by existing mbed-os tests (Greentea or Unittest)
[] Tests / results supplied as part of this PR

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Reviewers

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[jeromecoutant]

I don't see any issue

[0xc0170]

CI started

[mbed-ci]

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