base: unify syscall dependency to local path source

Change [workspace.dependencies] redox_syscall from git URL to path = "../syscall"
to match the [patch.crates-io] source. This eliminates the dual-source 0.8.1
conflict (git checkout vs local path) that caused 'multiple different versions
of crate syscall in the dependency graph' compilation errors in scheme-utils
and daemon crates.

The local fork at local/sources/syscall/ is upstream 79cb6d9 (0.8.1).

parking_lot_core 0.9.12 still pulls redox_syscall 0.5.18 from crates.io
(semver prevents the path patch from satisfying ^0.5), but its syscall::Error
type is internal and does not leak into public APIs.

Cargo.lock

@@ -1805,9 +1805,9 @@ dependencies = [
 
 [[package]]
 name = "rand"
-version = "0.8.5"
+version = "0.8.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "34af8d1a0e25924bc5b7c43c079c942339d8f0a8b57c39049bef581b46327404"
+checksum = "5ca0ecfa931c29007047d1bc58e623ab12e5590e8c7cc53200d5202b69266d8a"
 dependencies = [
  "libc",
  "rand_chacha 0.3.1",
@@ -1953,7 +1953,7 @@ dependencies = [
 [[package]]
 name = "redox-ioctl"
 version = "0.1.0"
-source = "git+https://gitlab.redox-os.org/redox-os/relibc.git#eeea60c1d1760a10ec5fb1fea2673f1a6e1cab14"
+source = "git+https://gitlab.redox-os.org/redox-os/relibc.git#15a4a27a467a5c355b2a6ac50f2cf26e33c251c2"
 dependencies = [
  "drm-sys",
  "redox_syscall 0.8.1",
@@ -2002,7 +2002,6 @@ dependencies = [
 [[package]]
 name = "redox_syscall"
 version = "0.8.1"
-source = "git+https://gitlab.redox-os.org/redox-os/syscall.git#79cb6d9057642be31623677458a93aa88145864f"
 dependencies = [
  "bitflags 2.13.0",
 ]
@@ -2505,7 +2504,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "97fee6b57c6a41524a810daee9286c02d7752c4253064d0b05472833a438f675"
 dependencies = [
  "cfg-if 1.0.4",
- "rand 0.8.5",
+ "rand 0.8.6",
  "static_assertions",
 ]