sim: drop common/cconfig.h in favor of a single config.h

sim: drop common/cconfig.h in favor of a single config.h

The common subdir sets up a cconfig.h file to hold checks for the common
code.  In practice, most files still end up using config.h instead which
just leads to confusion.

Merge all the configure checks that went into cconfig.h into SIM_AC_COMMON
so we can drop the cconfig.h file altogether.  Now there is only a single
config.h file like normal.