misc: Delete the now unnecessary create methods.

Most create() methods are no longer necessary. This change deletes them,
and occasionally moves some code from them into the constructors they
call.

Change-Id: Icbab29ba280144b892f9b12fac9e29a0839477e5
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/36536
Reviewed-by: Gabe Black <gabe.black@gmail.com>
Maintainer: Gabe Black <gabe.black@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/cpu/o3/SConscript

@@ -38,7 +38,6 @@ if 'O3CPU' in env['CPU_MODELS']:
     Source('base_dyn_inst.cc')
     Source('commit.cc')
     Source('cpu.cc')
-    Source('deriv.cc')
     Source('decode.cc')
     Source('dyn_inst.cc')
     Source('fetch.cc')