remove unused timer interrupt handler

raven/Makefile

@@ -3,7 +3,7 @@ TARGET    = hello_raven
 C_SRCS    = $(wildcard src/*.c)  $(BSP_BASE)/drivers/fe300prci/fe300prci_driver.c $(BSP_BASE)/drivers/plic/plic_driver.c
 CXX_SRCS  = $(wildcard src/*.cpp) 
 HEADERS   = $(wildcard src/*.h)
-CFLAGS    = -g -fno-builtin-printf -DUSE_PLIC -DUSE_M_TIME -DNO_INIT -I./src
+CFLAGS    = -g -fno-builtin-printf -DUSE_PLIC -I./src
 CXXFLAGS  = -fno-use-cxa-atexit
 LDFLAGS   = -Wl,--wrap=printf
 LDFLAGS  += -g -lstdc++ -fno-use-cxa-atexit -march=$(RISCV_ARCH) -mabi=$(RISCV_ABI) -mcmodel=medany