Remove override-stage

Current `override-stage` has no effect on final rock

I inspected the rock we're currently building (i.e. ghcr.io/canonical/charmed-mysql:8.0.37-22.04_edge), and it looks like it doesn't contain `/var/lib/mysql`
```
root@foo-0:/# find / -name mysql
/home/mysql
/usr/lib/x86_64-linux-gnu/perl5/5.34/DBD/mysql
/usr/lib/x86_64-linux-gnu/perl5/5.34/auto/DBD/mysql
/usr/lib/mysql
/usr/share/mysql
/usr/bin/mysql
/var/log/mysql
/etc/init.d/mysql
/etc/mysql
root@foo-0:/# mysqld --initialize-insecure -u mysql
root@foo-0:/# find / -name mysql
/home/mysql
/usr/lib/x86_64-linux-gnu/perl5/5.34/DBD/mysql
/usr/lib/x86_64-linux-gnu/perl5/5.34/auto/DBD/mysql
/usr/lib/mysql
/usr/share/mysql
/usr/bin/mysql
/var/log/mysql
/var/lib/mysql
/var/lib/mysql/mysql
/etc/init.d/mysql
/etc/mysql
```

so I think the entire `override-stage` in our rock is doing nothing

rockcraft.yaml

@@ -33,30 +33,6 @@ parts:
             - python3-yaml
         stage-snaps:
             - charmed-mysql/8.0/edge
-        override-stage: |
-            LIB_DIR=$CRAFT_STAGE/usr/lib/x86_64-linux-gnu
-            craftctl default
-            mkdir -p $CRAFT_STAGE/var/lib/mysql
-            ln -sf $LIB_DIR/libnuma.so.1 \
-                /usr/lib/x86_64-linux-gnu/libnuma.so.1
-            ln -sf $LIB_DIR/libaio.so.1 \
-                /usr/lib/x86_64-linux-gnu/libaio.so.1
-            ln -sf $LIB_DIR/libicuuc.so.70 \
-                /usr/lib/x86_64-linux-gnu/libicuuc.so.70
-            ln -sf $LIB_DIR/libicui18n.so.70 \
-                /usr/lib/x86_64-linux-gnu/libicui18n.so.70
-            ln -sf $LIB_DIR/libevent_core-2.1.so.7 \
-                /usr/lib/x86_64-linux-gnu/libevent_core-2.1.so.7
-            ln -sf $LIB_DIR/libevent_pthreads-2.1.so.7 \
-                /usr/lib/x86_64-linux-gnu/libevent_pthreads-2.1.so.7
-            ln -sf $LIB_DIR/libprotobuf-lite.so.23 \
-                /usr/lib/x86_64-linux-gnu/libprotobuf-lite.so.23
-            ln -sf $LIB_DIR/libicudata.so.70 \
-                /usr/lib/x86_64-linux-gnu/libicudata.so.70
-            rm -rf /var/lib/mysql/
-            mysqld --initialize
-            cp -r /var/lib/mysql $CRAFT_STAGE/var/lib
-            chown 584788:584788 $CRAFT_STAGE/var/lib/mysql
         override-prime: |
             craftctl default
             mv -f $CRAFT_PRIME/etc/mysql/mysql.cnf $CRAFT_PRIME/etc/mysql/my.cnf