nix-cli: Move nix2 binaries sources properly into nix subproject

There have been prior concerns about reogranizing the repo, but
this seems like a trivial simplification which will not interfere
with either our packaging or the modular builds in nixpkgs.

src/internal-api-docs/doxygen.cfg.in

@@ -57,9 +57,7 @@ INPUT                  = \
   @src@/libutil/args \
   @src@/libutil-tests \
   @src@/libutil-test-support/tests \
-  @src@/nix \
-  @src@/nix-env \
-  @src@/nix-store
+  @src@/nix
 
 # If the MACRO_EXPANSION tag is set to YES, doxygen will expand all macro names
 # in the source code. If set to NO, only conditional compilation will be

src/nix/build-remote

@@ -1 +0,0 @@
-../build-remote

src/nix/nix-build

@@ -1 +0,0 @@
-../nix-build

src/nix/nix-channel

@@ -1 +0,0 @@
-../nix-channel

src/nix/nix-collect-garbage

@@ -1 +0,0 @@
-../nix-collect-garbage

src/nix/nix-copy-closure

@@ -1 +0,0 @@
-../nix-copy-closure

src/nix/nix-env

@@ -1 +0,0 @@
-../nix-env

src/nix/nix-instantiate

@@ -1 +0,0 @@
-../nix-instantiate

src/nix/nix-store

@@ -1 +0,0 @@
-../nix-store/

src/nix/package.nix

@@ -33,15 +33,7 @@ mkMesonExecutable (finalAttrs: {
 
       # Symbolic links to other dirs
       ## exes
-      ./build-remote
       ./doc
-      ./nix-build
-      ./nix-channel
-      ./nix-collect-garbage
-      ./nix-copy-closure
-      ./nix-env
-      ./nix-instantiate
-      ./nix-store
       ## dirs
       ./scripts
       ../../scripts
@@ -55,8 +47,8 @@ mkMesonExecutable (finalAttrs: {
       ../../doc/manual/generate-store-info.nix
 
       # Other files to be included as string literals
-      ../nix-channel/unpack-channel.nix
-      ../nix-env/buildenv.nix
+      ./nix-channel/unpack-channel.nix
+      ./nix-env/buildenv.nix
       ./get-env.sh
       ./help-stores.md
       ../../doc/manual/source/store/types/index.md.in
@@ -65,24 +57,11 @@ mkMesonExecutable (finalAttrs: {
 
       # Files
     ]
-    ++
-      lib.concatMap
-        (dir: [
-          (fileset.fileFilter (file: file.hasExt "cc") dir)
-          (fileset.fileFilter (file: file.hasExt "hh") dir)
-          (fileset.fileFilter (file: file.hasExt "md") dir)
-        ])
-        [
-          ./.
-          ../build-remote
-          ../nix-build
-          ../nix-channel
-          ../nix-collect-garbage
-          ../nix-copy-closure
-          ../nix-env
-          ../nix-instantiate
-          ../nix-store
-        ]
+    ++ [
+      (fileset.fileFilter (file: file.hasExt "cc") ./.)
+      (fileset.fileFilter (file: file.hasExt "hh") ./.)
+      (fileset.fileFilter (file: file.hasExt "md") ./.)
+    ]
   );
 
   buildInputs = [