chore(librarian): remove docs/README.rst from preserve_regex (#14848)

As of #14751,
package level `docs/README.rst` files are included in the generated
output and are a copy of the package `README.rst`. We don't need to
preserve the existing version.

Author: parthea

.generator/cli.py

@@ -138,7 +138,6 @@ def _add_new_library_preserve_regex(library_config: Dict, library_id: str) -> No
         library_config["preserve_regex"] = [
             f"packages/{library_id}/CHANGELOG.md",
             "docs/CHANGELOG.md",
-            "docs/README.rst",
             "samples/README.txt",
             "scripts/client-post-processing",
             "samples/snippets/README.rst",

.generator/test-resources/librarian/build-request.json

@@ -26,7 +26,6 @@
     ".OwlBot.yaml",
     "packages/google-cloud-language/CHANGELOG.md",
     "docs/CHANGELOG.md",
-    "docs/README.rst",
     "samples/README.txt",
     "tar.gz",
     "scripts/client-post-processing"

.generator/test-resources/librarian/generate-request.json

@@ -26,7 +26,6 @@
     ".OwlBot.yaml",
     "packages/google-cloud-language/CHANGELOG.md",
     "docs/CHANGELOG.md",
-    "docs/README.rst",
     "samples/README.txt",
     "tar.gz",
     "scripts/client-post-processing"