build: remove -f{data,function}-sections flags

We don't link with `--gc-sections` because it's unreliable with some
toolchains, so all these flags do is make the compiler generate slightly
worse code.  Drop them.

Refs: https://github.com/nodejs/node/pull/6056
PR-URL: https://github.com/nodejs/node/pull/6077
Reviewed-By: Trevor Norris <trev.norris@gmail.com>

common.gypi

@@ -95,7 +95,7 @@
         'variables': {
           'v8_enable_handle_zapping': 0,
         },
-        'cflags': [ '-O3', '-ffunction-sections', '-fdata-sections' ],
+        'cflags': [ '-O3' ],
         'conditions': [
           ['target_arch=="x64"', {
             'msvs_configuration_platform': 'x64',