Remove many-many SpdyMajorVersion and NextProto arguments and members.

Now that SPDY/3.1 is disabled, rip it out from more areas of the code:

Remove SpdyMajorVersion and NextProto members, accessors, and function arguments
from BufferedSpdyFramer, SpdySession, SpdySessionPool, HeaderCoalescer,
SpdyStream classes, from spdy_http_utils.{h,cc}, and from flipserver.

Also deprecate Net.SpdySettingsCwndSent and Net.SpdyVersion3 histograms.

BUG=624095

Review-Url: https://codereview.chromium.org/2141993002
Cr-Commit-Position: refs/heads/master@{#405481}

• net/http/bidirectional_stream.cc[diff]
• net/http/bidirectional_stream_impl.h[diff]
• net/http/bidirectional_stream_unittest.cc[diff]
• net/http/http_network_session.cc[diff]
• net/http/http_network_session.h[diff]
• net/http/http_stream_factory_impl_job.cc[diff]
• net/quic/bidirectional_stream_quic_impl.cc[diff]
• net/quic/quic_http_stream.cc[diff]
• net/socket/ssl_client_socket_pool_unittest.cc[diff]
• net/spdy/bidirectional_stream_spdy_impl.cc[diff]
• net/spdy/bidirectional_stream_spdy_impl_unittest.cc[diff]
• net/spdy/buffered_spdy_framer.cc[diff]
• net/spdy/buffered_spdy_framer.h[diff]
• net/spdy/buffered_spdy_framer_unittest.cc[diff]
• net/spdy/header_coalescer.cc[diff]
• net/spdy/header_coalescer.h[diff]
• net/spdy/spdy_http_stream.cc[diff]
• net/spdy/spdy_http_stream_unittest.cc[diff]
• net/spdy/spdy_http_utils.cc[diff]
• net/spdy/spdy_http_utils.h[diff]
• net/spdy/spdy_http_utils_unittest.cc[diff]
• net/spdy/spdy_network_transaction_unittest.cc[diff]
• net/spdy/spdy_proxy_client_socket.cc[diff]
• net/spdy/spdy_proxy_client_socket_unittest.cc[diff]
• net/spdy/spdy_session.cc[diff]
• net/spdy/spdy_session.h[diff]
• net/spdy/spdy_session_pool.cc[diff]
• net/spdy/spdy_session_pool.h[diff]
• net/spdy/spdy_session_pool_unittest.cc[diff]
• net/spdy/spdy_session_unittest.cc[diff]
• net/spdy/spdy_stream.cc[diff]
• net/spdy/spdy_stream.h[diff]
• net/spdy/spdy_stream_unittest.cc[diff]
• net/spdy/spdy_test_util_common.cc[diff]
• net/tools/flip_server/sm_connection.cc[diff]
• net/tools/flip_server/sm_connection.h[diff]
• net/tools/flip_server/spdy_interface.cc[diff]
• net/tools/flip_server/spdy_interface.h[diff]
• net/tools/flip_server/spdy_interface_test.cc[diff]
• net/tools/quic/quic_in_memory_cache.cc[diff]
• net/tools/quic/quic_simple_client.cc[diff]
• net/tools/quic/quic_simple_client_bin.cc[diff]
• tools/metrics/histograms/histograms.xml[diff]