Deletion of codons at the start of a sequence in preparation for heterogeneous expression. Why?
The easiest answer would be to ask the authors of the patent. 
Several other possibilities (see comments) were excluded, such as:


restriction sites which interfere with cloning
signal peptide
proteolytic cleavage


Although it's just a theory, removing part of the N-terminus might improve protein stability and half-life time because the first 30-40 amino acids lack an ordered structure (as judged by submitting the structure to Phyre). Those structures are known to aggregate and influence protein stability.

References: 

The use of systematic N- and C-terminal deletions to promote production and structural studies of recombinant proteins.

Sequence composition of disordered regions fine-tunes protein half-life

Production of prone-to-aggregate proteins