How to disable Randomize in Firtool generated SV

I want to remove these randomzie lines generating at top of each SV output file.

// Generated by CIRCT unknown git version
// Standard header to adapt well known macros to our needs.
`ifdef RANDOMIZE_REG_INIT
  `define RANDOMIZE
`endif
`ifdef RANDOMIZE_MEM_INIT
  `define RANDOMIZE
`endif

// RANDOM may be set to an expression that produces a 32-bit random unsigned value.
`ifndef RANDOM
  `define RANDOM $random
`endif

Is there any flag that can be passed to firtool for this purpose?

No current flag, but we’re planning to add one soon! There’s a tracking issue about this here: [FIRRTL] Feature Request: Please support options for omission of the randomization code · Issue #4202 · llvm/circt · GitHub

One thing to note about this: if you’re using CIRCT as a mid/back-end for Chisel, these randomization statements may be necessary to simulate without hitting x-pessimism issues (or you may need to simulate with something like VCS x-prop turned on to give you less pessimistic behavior).