Drop dependency on SecurityManager

[edewata]

The Security Manager API was deprecated in JDK 17 so it should be removed from the code.

$ ./build.sh 
...
build-jdk:
    [javac] Compiling 155 source files to /home/edewata/build/ldapjdk/classes
    [javac] /home/edewata/Projects/ldap-sdk/java-sdk/ldapjdk/src/main/java/com/netscape/sasl/Sasl.java:249: warning: [removal] SecurityManager in java.lang has been deprecated and marked for removal
    [javac]         SecurityManager security = System.getSecurityManager();
    [javac]         ^
    [javac] /home/edewata/Projects/ldap-sdk/java-sdk/ldapjdk/src/main/java/com/netscape/sasl/Sasl.java:249: warning: [removal] getSecurityManager() in System has been deprecated and marked for removal
    [javac]         SecurityManager security = System.getSecurityManager();
    [javac]                                          ^
    [javac] /home/edewata/Projects/ldap-sdk/java-sdk/ldapjdk/src/main/java/netscape/ldap/LDAPCheckComm.java:56: warning: [removal] SecurityManager in java.lang has been deprecated and marked for removal
    [javac]       SecurityManager sec = System.getSecurityManager();
    [javac]       ^
    [javac] /home/edewata/Projects/ldap-sdk/java-sdk/ldapjdk/src/main/java/netscape/ldap/LDAPCheckComm.java:56: warning: [removal] getSecurityManager() in System has been deprecated and marked for removal
    [javac]       SecurityManager sec = System.getSecurityManager();
    [javac]                                   ^
    [javac] Note: Some input files use or override a deprecated API.
    [javac] Note: Recompile with -Xlint:deprecation for details.
    [javac] Note: Some input files use unchecked or unsafe operations.
    [javac] Note: Recompile with -Xlint:unchecked for details.
    [javac] 4 warnings
...
build-beans:
    [javac] Compiling 11 source files to /home/edewata/build/ldapjdk/classes
    [javac] /home/edewata/Projects/ldap-sdk/java-sdk/ldapbeans/src/main/java/netscape/ldap/beans/LDAPBasePropertySupport.java:291: warning: [removal] SecurityManager in java.lang has been deprecated and marked for removal
    [javac]         SecurityManager sec = System.getSecurityManager();
    [javac]         ^
    [javac] /home/edewata/Projects/ldap-sdk/java-sdk/ldapbeans/src/main/java/netscape/ldap/beans/LDAPBasePropertySupport.java:291: warning: [removal] getSecurityManager() in System has been deprecated and marked for removal
    [javac]         SecurityManager sec = System.getSecurityManager();
    [javac]                                     ^
    [javac] Note: /home/edewata/Projects/ldap-sdk/java-sdk/ldapbeans/src/main/java/netscape/ldap/beans/LDAPGetProperty.java uses unchecked or unsafe operations.
    [javac] Note: Recompile with -Xlint:unchecked for details.
    [javac] 2 warnings
...