rgw_main.cc: use static_cast instead of c-style

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
rgw_main.cc: remove unused variable

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
rgw_op.cc: remove unused map variable

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
KeyValueStore.cc: remove unused variable

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
PGBackend.cc: remove unused to_remove variable

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
rgw_admin.cc: remove unused string variable

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
rgw_common.cc: reduce scope of 'fpos' variable

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>