Remove symbol-observable and loose-envify deps

[markerikson]

This PR:

• Drops the legacy symbol-observable and loose-envify dependencies
• Inlines the symbol-observable polyfill

[codesandbox-ci]

This pull request is automatically built and testable in CodeSandbox.

To see build info of the built libraries, click here or the icon next to each commit SHA.

Latest deployment of this branch, based on commit d29cbfa:

Sandbox	Source
Vanilla	Configuration
Vanilla Typescript	Configuration

[github-actions]

Size Change: -523 B (1%)

Total Size: 27.1 kB

Filename	Size	Change
./dist/redux.js	7.99 kB	-389 B (4%)
./dist/redux.min.js	1.66 kB	-102 B (6%)	✅
./es/redux.js	7.87 kB	+47 B (0%)
./es/redux.mjs	1.57 kB	-112 B (7%)	✅
./lib/redux.js	8.03 kB	+33 B (0%)

_{compressed-size-action}