I tried to remove symbol using:

objcopy -v -I elf32-little -N <function> main_lib.so new_lib.so

On which it says:

copy from `main_lib.so' [elf32-little] to `new_lib.so' [elf32-little]

There is no change between the two files, and the function is not removed.

I used to following commands to get the list of functions and format:

readelf -Ws main_lib.so > main_functions.txt
file main_lib.so

File command says:

main_lib.so: ELF 32-bit LSB  shared object, ARM, EABI5 version 1 (SYSV),
dynamically linked (uses shared libs), BuildID[md5/uuid]=..., stripped