[SPDY] Remove references to obsolete SPDY versions SPDY/1 and SPDY/2.1

Remove them from NextProto and AlternateProtocol enums.

Add constants for minimum/maximum/number of valid AlternateProtocol
enum values and use that consistently.

Take care of TODOs to use kProtoSPDYMinimumVersion instead of
kProtoSPDY2 (since they're now one and the same).

BUG=303957
R=rtenneti@chromium.org

Review URL: https://codereview.chromium.org/25956002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@227043 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 227043
Revert 226390 "Land Recent QUIC changes."

> Land Recent QUIC changes.
> 
> Fixing minor nits (added using std::pair).
> 
> Merge internal change: 53257699
> 
> Increasing the maximum tcp congestion window to 200 packets from 100.
> 
> Merge internal change: 53185276
> 
> Add a DCHECK to ensure the sent packet sequence number never goes down
> and separate the send alarm into a send alarm and a resume writes
> alarm to be used when the socket is still writable an there may be
> more pending data to write.
> 
> Merge internal change: 53050471
> 
> Merged quic_epoll_connection_helper_test.cc from internal code.
> 
> Minor nit fixes.
> 
> Merge internal change: 53048224
> 
> Move QuicAckNotifierManager from QuicConnection to
> QuicSentPacketManager.
> 
> Merge internal change: 53036185
> 
> R=jar@chromium.org, rch@chromium.org, wtc@chromium.org
> 
> Review URL: https://codereview.chromium.org/25443002

TBR=rtenneti@chromium.org
BUG=303981

Review URL: https://codereview.chromium.org/25727012

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@227044 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 227044