dual clock sdc exist, causing TCLCMD-1594 error

[cedard234]

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Fix duplicate create_clock warning in PAR (TCLCMD-1594/958)

When a post-synthesis SDC (gcd.mapped.sdc) is present, Hammer's MMMC script loaded both clock_constraints_fragment.sdc (generated from vlsi.inputs.clocks) and the synthesis SDC, both of which define create_clock for the same clock. This caused Innovus to warn that the clock definition was being overwritten.

Fix: in generate_mmmc_script(), filter out clock_constraints_fragment.sdc from the SDC list when a post-synthesis SDC is present, since the synthesis SDC already carries the clock definition. The pin constraints fragment is still included. Behavior is unchanged when no post-synthesis SDC exists (e.g. running PAR standalone).