refactor(controller,xceadmin): drop generic Resource.unit, hardcode bytes for maxmem

Simplification per review feedback on e3b3ffa: a generic schema-driven
unit field touched the capnp wire schema (2 structs), C structs
(xce_resource_t/xce_resval_t), resobj.c's deep-copy/destroy, opget.c's
reply-build lookup, resources.yaml/resources.schema.json, and mapping.py
-- real cross-cutting cost for a mechanism only one resource (maxmem)
actually needs today.

Reverted all of that. The controller CLI (test.c) now just knows
"maxmem" is bytes-valued via a small explicit is_bytes_valued_resource()
name list, and adaptively picks the best-fit human unit at display time
(format_bytes_human, unchanged) -- same observable behavior (resval/
workerlist render maxmem as e.g. "30.90 GB"), zero wire schema surface.
Regenerated the xceadmin golden fixture back to its pre-unit-field size
(5304 bytes, exactly matching the size right after the mxj-only fix,
confirming a clean, complete removal).

Verified: 1095/1095 controller_unit_test (3 runs; one hit the
pre-existing flaky segfault already logged as bug-1553, unrelated),
228/228 xceadmin pytest, clean rebuild of lib/controller/xceadmin/xce_test.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/configs/resources.yaml

@@ -58,7 +58,6 @@ resources:
 
   - name: maxmem
     type: numeric
-    unit: bytes
     description: "max memory in bytes (built-in host attribute; CLI display converts to a human-readable unit)"
 
   - name: maxswap

src/configs/schema/resources.schema.json

@@ -13,7 +13,6 @@
           "consumable":  { "type": "boolean" },
           "release":     { "type": "boolean" },
           "description": { "type": "string" },
-          "unit":        { "type": "string", "enum": ["bytes"], "description": "Display-unit hint for CLI/UI formatting; the stored value itself is always in this unit, never converted at rest. Omit for a plain unitless number (the default for every existing resource)." },
           "resourcemap": {
             "type": "array",
             "items": {