Remove unused sourcemapper.js tools. NFC (emscripten-core#14218)

The last use of this tools was removed when the emit_js_source_maps
function was removed from emcc.py in emscripten-core#13599.

The source-map npm module is now only used by the sourcemap2json.js test
script so moved to devDependencies.

Author: sbc100

package-lock.json

@@ -4,13 +4,13 @@
     "es-check": "^5.2.3",
     "eslint": "^7.26.0",
     "eslint-config-google": "^0.14.0",
+    "source-map": "0.5.6",
     "ws": "~0.4.28"
   },
   "dependencies": {
     "acorn": "7.3.1",
     "google-closure-compiler": "20200920.0.0",
     "html-minifier-terser": "5.0.2",
-    "source-map": "0.5.6",
     "wasm2c": "1.0.0"
   },
   "scripts": {

package.json

@@ -7125,7 +7125,7 @@ def test_source_map(self, args):
       # needs to containt valid source text.
       self.assertTextDataIdentical(src, data['sourcesContent'][0])
     mappings = json.loads(self.run_js(
-      path_from_root('tools/source-maps/sourcemap2json.js'),
+      path_from_root('tests/sourcemap2json.js'),
       args=[map_filename]))
     seen_lines = set()
     for m in mappings: