Portduino-buildroot: Remove pkg-config optional libs (#5573)

variants/portduino-buildroot/platformio.ini

@@ -1,11 +1,9 @@
 [env:buildroot]
 extends = portduino_base
-; The pkg-config commands below optionally add link flags.
-; the || : is just a "or run the null command" to avoid returning an error code
+; Optional libraries should be appended to `PLATFORMIO_BUILD_FLAGS`
+; environment variable in the buildroot environment.
 build_flags = ${portduino_base.build_flags} -O0 -I variants/portduino-buildroot
   -std=c++17
-  !pkg-config --libs libulfius --silence-errors || :
-  !pkg-config --libs openssl --silence-errors || :
 board = buildroot
 lib_deps = ${portduino_base.lib_deps}
 build_src_filter = ${portduino_base.build_src_filter}