[LineProgram] Don't make LineEncoding configurable

[bjorn3]

This would likely make it possible for LLVM to optimize a division away which accounts for ~30% of the time in generate_row. I don't see much use for it anyway.

gimli/src/write/line.rs

Line 471 in 1e49ffc

self.row.address_offset % u64::from(self.line_encoding.minimum_instruction_length),

and

gimli/src/write/line.rs

Line 475 in 1e49ffc

/ u64::from(self.line_encoding.minimum_instruction_length);

[philipc]

Alternatively, we could do something like 35c7750 and rely on branch prediction.