So, which modules are included in your "cross-compile bundle"? (Hint, it will be documented in one of the build scripts.) Once you have that list of all the modules, determine which modules your code uses (Hint: you use modules) and cross them off the list. Look at each of these modules, determine their pre/co requisits and cross them off as well. Repeat this process. The remaining items on the list after all of the direct-, pre-, and co-requisites are subracted are candidates for removal.

Start removing them, one at a time, and verify between each removal that the code still works properly (Hint: use your extensive test suit). If the code still works, congratualations, you have found a 'unnecessary' module. Repeat process for the rest of your list.

Or, you could just buy a better hard-drive....

Note: the 'unecessary modules' list you build here is good only for this particular version of your Code. The first time you try to add a feature, you may well discover that you need to add another module.

You are creating a maintenance nightmare as a trade for a few megabytes of storage. In the age of multi-TByte disks and laptops with 500G of main memory, you are being "penny-wise and pound-foolish".

Update: Corrected typo (Thanks MidLifeXis)