v8: remove optimization switches

Remove compiler switches from $(TOPLEVEL)/deps/v8/build/common.gypi,
we set them globally in $(TOPLEVEL)/common.gypi.

Commit 7b4d95a introduced the switches again, resulting in V8 getting
built without any optimizations.

This commit is essentially a rehash of commit 4b8629d.

deps/v8/build/common.gypi

@@ -399,15 +399,6 @@
           }],
           ['OS=="linux" or OS=="freebsd" or OS=="openbsd" or OS=="netbsd" \
             or OS=="android"', {
-            'cflags!': [
-              '-O2',
-              '-Os',
-            ],
-            'cflags': [
-              '-fdata-sections',
-              '-ffunction-sections',
-              '-O3',
-            ],
             'conditions': [
               [ 'gcc_version==44 and clang==0', {
                 'cflags': [