fix: Revert "feat: add p/nestedpkg (gnolang#2342)" (gnolang#2525)

## Description

This PR reverts commit 77ceda4, gnolang#2342, because of a cyclic `gno.mod`
import that's causing the node to not be able to generate genesis
transactions and start.

<details><summary>Contributors' checklist...</summary>

- [x] Added new tests, or not needed, or not feasible
- [x] Provided an example (e.g. screenshot) to aid review or the PR is
self-explanatory
- [x] Updated the official documentation or not needed
- [x] No breaking changes were made, or a `BREAKING CHANGE: xxx` message
was included in the description
- [x] Added references to related issues and PRs
- [ ] Provided any useful hints for running manual tests
- [ ] Added new benchmarks to [generated
graphs](https://gnoland.github.io/benchmarks), if any. More info
[here](https://github.com/gnolang/gno/blob/master/.benchmarks/README.md).
</details>

examples/gno.land/r/demo/tests/gno.mod

@@ -1,6 +1,3 @@
 module gno.land/r/demo/tests
 
-require (
-	gno.land/p/demo/nestedpkg v0.0.0-latest
-	gno.land/r/demo/tests/subtests v0.0.0-latest
-)
+require gno.land/r/demo/tests/subtests v0.0.0-latest

examples/gno.land/r/demo/tests/tests.gno

@@ -3,7 +3,6 @@ package tests
 import (
 	"std"
 
-	"gno.land/p/demo/nestedpkg"
 	rsubtests "gno.land/r/demo/tests/subtests"
 )
 
@@ -100,15 +99,3 @@ func GetRSubtestsPrevRealm() std.Realm {
 func Exec(fn func()) {
 	fn()
 }
-
-func IsCallerSubPath() bool {
-	return nestedpkg.IsCallerSubPath()
-}
-
-func IsCallerParentPath() bool {
-	return nestedpkg.IsCallerParentPath()
-}
-
-func HasCallerSameNamespace() bool {
-	return nestedpkg.IsSameNamespace()
-}