gen_compile_commands.py: remove code for '\#' replacement

Since commit 9564a8cf ("Kbuild: fix # escaping in .cmd files for
future Make"), '#' in the build command is replaced with $(pound) rather
than '\#'.

Calling .replace(r'\#', '#') is only necessary when this tool is used
to parse .*.cmd files generated by Linux 4.16 or earlier, which is
unlikely to happen.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>