Switch plugin packages back to git submodules (#678)

Alright, so I hate to be the one to do this, but #584 broke crates.io
publishing and also caused librojo to be unusable. I see that there was
some discussion on Discord shortly after the problem was realized, but
there was no action taken.

I think keeping librojo and publishing working far, far outweigh any
convenience added by Wally.

I've kept the same `Packages` naming convention to keep the diff
minimal.

plugin/test-place.project.json

@@ -9,7 +9,7 @@
       },
 
       "Packages": {
-        "$path": "DevPackages"
+        "$path": "Packages"
       }
     },
 

plugin/wally.lock

@@ -1,33 +0,0 @@
-# This file is automatically @generated by Wally.
-# It is not intended for manual editing.
-registry = "test"
-
-[[package]]
-name = "evaera/promise"
-version = "4.0.0"
-dependencies = []
-
-[[package]]
-name = "osyrisrblx/t"
-version = "3.0.0"
-dependencies = []
-
-[[package]]
-name = "reselim/flipper"
-version = "2.0.0"
-dependencies = []
-
-[[package]]
-name = "roblox/roact"
-version = "1.4.4"
-dependencies = []
-
-[[package]]
-name = "roblox/testez"
-version = "0.4.1"
-dependencies = []
-
-[[package]]
-name = "rojo-rbx/rojo"
-version = "7.3.0"
-dependencies = [["Flipper", "reselim/flipper@2.0.0"], ["Promise", "evaera/promise@4.0.0"], ["Roact", "roblox/roact@1.4.4"], ["t", "osyrisrblx/t@3.0.0"]]

plugin/wally.toml

@@ -1,17 +0,0 @@
-[package]
-name = "rojo-rbx/rojo"
-description = "Rojo enables Roblox developers to use professional-grade software engineering tools"
-version = "7.3.0"
-license = "MPL-2.0"
-authors = ["LPGhatguy (https://lpg.space/)"]
-registry = "https://github.com/upliftgames/wally-index"
-realm = "shared"
-
-[dependencies]
-Flipper = "reselim/flipper@2.0.0"
-Promise = "evaera/promise@4.0.0"
-Roact = "roblox/roact@1.4.4"
-t = "osyrisrblx/t@3.0.0"
-
-[dev-dependencies]
-TestEZ = "roblox/testez@0.4.1"