Support dropping named partitions in hardware configs

[mikee47]

This PR adds the ability to 'drop' a previously defined partition from a hardware configuration by setting "size": 0 in an inherited config. This is silently ignored if the partition is undefined.

Issue #2933 highlighted the need to be able to eliminate the factory partition and use OTA partitions instead.

A couple of sample applications contained redundant subtype overrides since these are already defined in spiffs-two-roms, so this has been tidied.

Note: Typically the Esp32 spiffs-two-roms configuration is used as a base for OTA updates. This retains the factory partition so if not required this can be dropped to liberate the 1M allocation.

[what-the-diff]

PR Summary

• Change in Factory Partition Size
  The size of the 'factory' partition in spiffs-two-roms.hw has been lowered to 0, effectively removing it.

• Documentation Update in README.rst
  The README.rst has been updated to clarify that if the 'factory' partition size is set to 0, it will be ignored if no such partition exists.

• Update in partition.py Logic
  The partition.py script now has new logic to automatically remove a partition if its size is set to 0.

• Simplified Validation Process in partition.py
  The verification method in partition.py has been adjusted to avoid error messages if the size is 0, making validation easier and simpler.

• Configuration Switch in component.mk
  The HWCONFIG in component.mk has been switched from ota to spiffs-two-roms, adopting the updated configuration.

• Removal of Deprecated OTA Settings
  The ota.hw file, which carried obsolete OTA configuration settings, has been deleted.

• Clean-up in Basic_Ota Sample File
  The ota.hw file in the Basic_Ota sample has been cleaned up, removing redundant OTA partition definitions for 'rom0' and 'rom1'.

[slaff]

@mikee47 ready with this one?

[mikee47]

@slaff Yes, all done thanks.