Bug 28904: remove network.http.spdy.enabled prefs
Bug 28904: remove network.http.spdy.enabled prefs

network.http.spdy.enabled, network.http.spdy.enabled.v2 and
network.http.spdy.enabled.v3 have been removed in bug 14952.

boklm/tbb-testsuite,boklm/tbb-testsuite,boklm/tbb-testsuite,boklm/tbb-testsuite,boklm/tbb-testsuite