Revert "build,test: add duplicate symbol test"

This reverts commit 2761afb.

Building with `-fvisibility=hidden` breaks some of Node's add-on tests
and therefore likely also affects third-party add-ons. This change was
landed in a patch release so I'm opting to revert it until the next
major release.

PR-URL: #1828
Refs: nodejs/node#28647 (comment)
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Rod Vagg <rod@vagg.org>

addon.gypi

@@ -90,14 +90,10 @@
 
     'conditions': [
       [ 'OS=="mac"', {
-        'cflags': [
-          '-fvisibility=hidden'
-        ],
         'defines': [
           '_DARWIN_USE_64_BIT_INODE=1'
         ],
         'xcode_settings': {
-          'GCC_SYMBOLS_PRIVATE_EXTERN': 'YES', # -fvisibility=hidden
           'DYLIB_INSTALL_NAME_BASE': '@rpath'
         },
       }],

test/test-addon.js

@@ -18,15 +18,6 @@ function runHello (hostProcess) {
   return execFileSync(hostProcess, [ '-e', testCode ], { cwd: __dirname }).toString()
 }
 
-function runDuplicateBindings () {
-  const hostProcess = process.execPath
-  var testCode =
-    'console.log((function(bindings) {' +
-    'return bindings.pointerCheck1(bindings.pointerCheck2());' +
-    "})(require('duplicate_symbols')))"
-  return execFileSync(hostProcess, [ '-e', testCode ], { cwd: __dirname }).toString()
-}
-
 function getEncoding () {
   var code = 'import locale;print(locale.getdefaultlocale()[1])'
   return execFileSync('python', [ '-c', code ]).toString().trim()
@@ -60,21 +51,6 @@ test('build simple addon', function (t) {
   proc.stderr.setEncoding('utf-8')
 })
 
-test('make sure addon symbols do not overlap', function (t) {
-  t.plan(3)
-
-  var addonPath = path.resolve(__dirname, 'node_modules', 'duplicate_symbols')
-  // Set the loglevel otherwise the output disappears when run via 'npm test'
-  var cmd = [nodeGyp, 'rebuild', '-C', addonPath, '--loglevel=verbose']
-  execFile(process.execPath, cmd, function (err, stdout, stderr) {
-    var logLines = stderr.trim().split(/\r?\n/)
-    var lastLine = logLines[logLines.length - 1]
-    t.strictEqual(err, null)
-    t.strictEqual(lastLine, 'gyp info ok', 'should end in ok')
-    t.strictEqual(runDuplicateBindings().trim(), 'not equal')
-  })
-})
-
 test('build simple addon in path with non-ascii characters', function (t) {
   t.plan(1)