Remove unnecessary checking and casting of sizeof when we need uint16_t sizes

[bzbarsky-apple]

Compilers generate a constant for sizeof(), which converts cleanly to
whatever integer size we need as long as the constant is small enough.

Problem

We have extra complexity we do not need.

Summary of Changes

Remove the complexity.

[github-actions]

Size increase report for "gn_qpg6100-example-build" from d48bcf2

File	Section	File	VM
chip-qpg6100-lock-example.out	.text	-104	-104

Full report output

BLOAT REPORT

Files found only in the build output:
    report.csv

Comparing ./master_artifact/chip-qpg6100-lock-example.out and ./pull_artifact/chip-qpg6100-lock-example.out:

sections,vmsize,filesize
[Unmapped],0,104
.debug_aranges,0,-24
.debug_ranges,0,-24
.symtab,0,-32
.debug_frame,0,-52
.debug_abbrev,0,-83
.text,-104,-104
.debug_loc,0,-205
.debug_line,0,-237
.debug_info,0,-499