cephfs-top: Removes unused global statements

Recent flake8 runs were failing with:
```
py3: flake8==7.2.0,mccabe==0.7.0,pip==25.0.1,pycodestyle==2.13.0,pyflakes==3.3.0,setuptools==75.8.0,wheel==0.45.1
py3: commands[0] /home/jenkins-build/build/workspace/ceph-pull-requests/src/tools/cephfs/top> flake8 --ignore=W503 --max-line-length=100 cephfs-top
cephfs-top:344:9: F824 `global fs_list` is unused: name is never assigned in scope
cephfs-top:466:13: F824 `global current_states` is unused: name is never assigned in scope
cephfs-top:872:9: F824 `global metrics_dict` is unused: name is never assigned in scope
cephfs-top:872:9: F824 `global current_states` is unused: name is never assigned in scope
cephfs-top:911:9: F824 `global fs_list` is unused: name is never assigned in scope
cephfs-top:981:9: F824 `global current_states` is unused: name is never assigned in scope
cephfs-top:1126:13: F824 `global current_states` is unused: name is never assigned in scope
py3: exit 1 (0.77 seconds) /home/jenkins-build/build/workspace/ceph-pull-requests/src/tools/cephfs/top> flake8 --ignore=W503 --max-line-length=100 cephfs-top pid=2309605
  py3: FAIL code 1 (8.15=setup[7.38]+cmd[0.77] seconds)
  evaluation failed :( (8.24 seconds)
```

Since these variables are only being referenced and not assigned within
their scopes, the `global` declarations are unnecessary and can be
safely removed. This change:

- Removes all flagged `global` statements
- Fixes the failing flake8 checks in the CI pipeline
- Maintains the original code behavior as variable references still work without the `global` keyword

The `global` keyword is only needed when assigning to global variables
within a function scope, not when simply referencing them.

Signed-off-by: Kefu Chai <[email protected]>

Author: tchaikov

src/tools/cephfs/top/cephfs-top

@@ -341,7 +341,6 @@ class FSTop(FSTopBase):
         except Exception as e:
             raise FSTopException(f'Error in fs ls: {e}')
         fs_map = json.loads(buf.decode('utf-8'))
-        global fs_list
         fs_list.clear()
         for filesystem in fs_map:
             fs = filesystem['name']
@@ -463,7 +462,7 @@ class FSTop(FSTopBase):
         key = 0
         endwhile = False
         while not endwhile:
-            global current_states, fs_list
+            global fs_list
             fs_list = self.get_fs_names()
 
             if key == curses.KEY_UP and curr_row1 > 0:
@@ -869,7 +868,6 @@ class FSTop(FSTopBase):
                 xp += len(self.items(item)) + ITEMS_PAD_LEN
 
     def create_clients(self, stats_json, fs_name):
-        global metrics_dict, current_states
         counters = [m.upper() for m in stats_json[GLOBAL_COUNTERS_KEY]]
         self.tablehead_y += 2
         res = stats_json[GLOBAL_METRICS_KEY].get(fs_name, {})
@@ -908,7 +906,6 @@ class FSTop(FSTopBase):
         if not stats_json['version'] == FS_TOP_SUPPORTED_VER:
             self.header.addstr(0, 0, 'perf stats version mismatch!', curses.A_BOLD)
             return False
-        global fs_list
         for fs_name in fs_list:
             client_metadata = stats_json[CLIENT_METADATA_KEY].get(fs_name, {})
             client_cnt = len(client_metadata)
@@ -978,7 +975,7 @@ class FSTop(FSTopBase):
 
         curses.halfdelay(1)
         cmd = self.stdscr.getch()
-        global fs_list, current_states
+        global fs_list
         while not self.exit_ev.is_set():
             fs_list = self.get_fs_names()
             fs = current_states["last_fs"]
@@ -1123,7 +1120,7 @@ class FSTop(FSTopBase):
                     self.exit_ev.set()
 
             # header display
-            global fs_list, current_states
+            global fs_list
             fs_list = self.get_fs_names()
             current_states["last_fs"] = fs_list
             stats_json = self.perf_stats_query()