Non-ABI builds are intended only for embeddded systems such as
HWW/homebrew devices, and aren't supported by wrapped languages.

Note that the tests for this configuration are supported; users
can still verify the library functionality for this build config.

Use the now-exposed transaction member accessors so that the test
does not rely on the binary layout of the transaction struct which
changes when the Elements ABI is disabled.

Notably, secp no longer uses a generated config header, and embedded builds
need to #define the modules they wish to use.

Remove unused config #define references, and use warning #pragmas
to avoid warnings rather than dummy functions.

For the windows build/batch files, build using the amalgamation rather than
having to define a large number of config defines on the command line.
Use the above changes to greatly simplify both windows wheel builds and
building wally as a DLL.

We only need our config.h and the swig wrapper, so skip building the
entire library only to rebuild it again via the amalgamation.

…gnore

Due to how secp now handles dllexport, it is no longer possible to build
static and shared libraries under windows in a single invocation.