Remove pointless redefinition of 'privoxy_mutex_t'

Remove pointless redefinition of 'privoxy_mutex_t'

... when compiling with FEATURE_HTTPS_INSPECTION.

Silences warnings when compiling with "-std=c99":

    cc -c -pipe -fstack-protector-all -ggdb -Wshadow  -Wconversion -I/usr/local/include/  -pthread -Wall -std=c99   errlog.c -o errlog.o
    In file included from errlog.c:70:
    ./jcc.h:66:25: warning: redefinition of typedef 'privoxy_mutex_t' is a C11 feature [-Wtypedef-redefinition]
    typedef pthread_mutex_t privoxy_mutex_t;
                            ^
    ./project.h:59:28: note: previous definition is here
       typedef pthread_mutex_t privoxy_mutex_t;
                               ^
    1 warning generated.

Compile-tested on Windows by Lee.