SYSML2_ — Remove "Connection" from the names "FlowConnectionDefinition", "FlowConnectionUsage", and "SuccessionFlowConnectionUsage"

After resolution SYSML2_-403 to issue SYSML2_-173, FlowConnectionDefinition no longer specializes ConnectionDefinition (now specializing only ActionDefinition and KerML Interaction), and FlowConnectionUsage no longer specializes ConnectionUsage (now only specializing ActionUsage, ConnectorAsUsage and KerML ItemFlow. As a result of SYSML2_-403, having "Connection" in the name of the "Flow" classes causesconfusion among users that don't see the distinction between structure and behavior.

Renaming FlowConnectionDefinition to FlowDefinition and FlowConnectionUsage to FlowUsage would avoid confusion going forward. Not making this change prior to finalization of SysML v2 runs the risk of having confusion that would require complex deprecation steps to correct later.

Similarly for SuccessionFlowConnectionUsage, which specializes FlowConnectionUsage.