pybind: Remove unneeded suppression of #warnings (Resolves RobotLoc…

…omotion#8437)

This was done before because our fork of `pybind11` included NumPy headers
to support dtype=object, but did not add the directive to not use
deprecated features. They should not be necessary now.

tools/skylark/pybind.bzl

@@ -22,7 +22,6 @@ _PY_VERSION = "2.7"
 def _drake_pybind_cc_binary(
         name,
         srcs = [],
-        copts = [],
         deps = [],
         visibility = None,
         testonly = None):
@@ -38,12 +37,6 @@ def _drake_pybind_cc_binary(
         name = name,
         # This is how you tell Bazel to link in a shared library.
         srcs = srcs + ["//tools/install/libdrake:libdrake.so"],
-        # These copts are per pybind11 deficiencies.
-        copts = [
-            "-Wno-#warnings",
-            "-Wno-cpp",
-            "-Wno-unknown-warning-option",
-        ] + copts,
         # This is how you tell Bazel to create a shared library.
         linkshared = 1,
         linkstatic = 1,
@@ -66,7 +59,6 @@ def drake_pybind_library(
         name,
         cc_srcs = [],
         cc_deps = [],
-        copts = [],
         cc_so_name = None,
         package_info = None,
         py_srcs = [],