Remove checks for old Meson

  We require 0.56.0 now.
Remove deprecated Meson call
Update calls to pkgconfig.generate

  The library to wrap should be passed as first positional argument, and we can

  pass actual dependencies as the runtime requirements. We can't pass things that

  might be subprojects as dependencies, which may be a Meson bug, so pass those

  ones as strings.

Re-configured and looked at the pkgconfig files.