Include $(BUILD_NUMBER_FROM_FILE) in the toybox --version.

Include $(BUILD_NUMBER_FROM_FILE) in the toybox --version.

Also remove the SHA, which we haven't needed yet and isn't particularly
easy to turn back into source anyway.

Also switch to sed rather than awk, because macOS awk is lame:

  awk: syntax error at source line 1
   context is
          match($0, >>>  /TOYBOX_VERSION.*"(.*)"/, <<<
  awk: bailing out at source line 1

Bug: http://b/27534935 (for the macOS awk problem)
Test: toybox --version
Change-Id: If2d86b1ef098f1710843e32f7345ae5cf251fabb