auto/otel: Remove pkg-config check

[ac000]

    auto/otel: Remove pkg-config check

    @thresheek reported an issue trying to configure OTEL support on Amazon
    Linux 2
    
      checking for OTEL requirements:
        - checking for rust compiler ... found
        - checking for cargo ... found
        - checking for OpenSSL library ... found
      Package openssl was not found in the pkg-config search path.
      Perhaps you should add the directory containing `openssl.pc'
      to the PKG_CONFIG_PATH environment variable
      No package 'openssl' found
    
    We successfully built the test program with '-lssl -lcrypto', but then
    tried to use 'pkg-config openssl --cflags --libs' to override
    NXT_OTEL_LIBS.
    
    On Amazon Linux2 there is no openssl.pc, they have a openssl11.pc.
    
    Let's just remove the pkg-config check, if we get here, we have
    successfully built with '-lssl -lcrypto', so just go with that (it also
    matches what we do in auto/ssltls).
    
    Closes: https://github.com/nginx/unit/issues/1510
    Signed-off-by: Andrew Clayton <a.clayton@nginx.com>

[thresheek]

I agree with reasoning in #1510 (comment) - this pkg-config call actually shouldnt be required if we already linked with openssl. And if we failed, a caller needs to provide proper --cc-opt and --ld-opt.

LGTM