[packages] Restore remote shorthand vars and !remove in early package contents validation (#12158)

Co-authored-by: J. Nick Koston <nick@koston.org>

tests/unit_tests/fixtures/substitutions/06-remote_packages.approved.yaml

@@ -23,3 +23,8 @@ values_from_repo1_main:
     y: 10
     z: 11
     volume: 990
+  - package_name: default
+    x: 10
+    y: 20
+    z: 5
+    volume: 1000

tests/unit_tests/fixtures/substitutions/06-remote_packages.input.yaml

@@ -35,3 +35,9 @@ packages:
           b: 10
           c: 11
     ref: main
+  package5: !include
+    file: remote_package_shorthand.yaml
+    vars:
+      repo: repo1
+      file: file1.yaml
+      ref: main

tests/unit_tests/fixtures/substitutions/remote_package_shorthand.yaml

@@ -0,0 +1,4 @@
+# acts as a proxy to be able to include a remote package
+# in which the shorthand comes from a substitution
+packages:
+  - github://esphome/${repo}/${file}@${ref}