clean: remove outdated microbundle cache directories

- microbundle hasn't used these directories in 3+ years
  - https://github.com/developit/microbundle/commit/d0e66da9578ee36b8e629039372e9f253ed053fa
- and rollup-plugin-typescript2, which microbundle depends on and which
  actually created the dirs, hasn't used them in ~3 years either
  - https://github.com/ezolenko/rollup-plugin-typescript2/commit/ffda2e539bf076da00d5093829a5a20a50a0f58d

- I help maintain rpt2 and formerly solo-maintained TSDX for ~1.5 years,
  which, as a fork of microbundle, has similarly used those directories
  in the past until I changed them
  - https://github.com/jaredpalmer/tsdx/commit/55c0d47c0bbee16bb780e8aa9441ca426ba127c7

Node.gitignore

@@ -57,12 +57,6 @@ web_modules/
 # Optional stylelint cache
 .stylelintcache
 
-# Microbundle cache
-.rpt2_cache/
-.rts2_cache_cjs/
-.rts2_cache_es/
-.rts2_cache_umd/
-
 # Optional REPL history
 .node_repl_history