Remove unused JS globals for stdin/stdout/stderr

[sbc100]

These globals are defined in musl C code so as far as I can tell
are never used.

[sbc100]

Am I missing something?

[sbc100]

Looks like these variable go back to 16f60de, but I don't see them used today

[kripken]

I think these might be leftovers from when we did more of that in JS, yes.

(However, that one other test failure makes me worry we are missing something?)

[sbc100]

Looks like we have a test there is hyper sensitve to size of static data:

FAIL: test_clear_error_on_massive_static_data (test_other.other)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/usr/lib/python3.5/unittest/case.py", line 58, in testPartExecutor
    yield
  File "/usr/lib/python3.5/unittest/case.py", line 600, in run
    testMethod()
  File "/root/emscripten/tests/test_other.py", line 8232, in test_clear_error_on_massive_static_data
    self.assertContained('Memory is not large enough for static data (134032) plus the stack (1024), please increase TOTAL_MEMORY (65536)', err)
  File "/root/emscripten/tests/runner.py", line 712, in assertContained
    additional_info
  File "/usr/lib/python3.5/unittest/case.py", line 665, in fail
    raise self.failureException(msg)
AssertionError: Expected to find 'Memory is not large enough for static data (134032) plus the stack (1024), please increase TOTAL_MEMORY (65536)' in 'shared:ERROR: Memory is not large enough for static data (133984) plus the stack (1024), please increase TOTAL_MEMORY (65536) to at least 136032
', diff:

Will fix.

[sbc100]

Also, makeStaticAlloc default to 16 byte alignment so this saves 48 bytes (in the debug build only I guess)