Remove redundant decls

[haochengxia]

Since -Wredundant-decls is enabled, we get error msg like

libCacheSim/cache/admission/adaptsize/adaptsize_interface.cpp:28:23: error: redundant redeclaration of ‘admissioner_t* create_adaptsize_admissioner(const char*)’ in same scope [-Werror=redundant-decls]
   28 | extern admissioner_t *create_adaptsize_admissioner(const char *init_params); // declared in admissionAlgo.h
   
libCacheSim/cache/admission/adaptsize/adaptsize_interface.cpp:6:
libCacheSim/cache/admission/../../include/libCacheSim/admissionAlgo.h:31:16: note: previous declaration of ‘admissioner_t* create_adaptsize_admissioner(const char*)’
   31 | admissioner_t *create_adaptsize_admissioner(const char *init_params);
      |                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~