Update d.py to 1.6.0, aiohttp to 3.7.3, Red-Lavalink to 0.7.2 (#4728)

* Bump d.py, aiohttp, Red-Lavalink

* Remove deprecation warnings that are no longer relevant

* Max concurrency things in `Command.prepare()`

* Two random things that date back to times older than d.py 1.1...

setup.cfg

@@ -32,7 +32,7 @@ classifiers =
 packages = find_namespace:
 python_requires = >=3.8.1,<3.9
 install_requires =
-    aiohttp==3.6.2
+    aiohttp==3.7.3
     aiohttp-json-rpc==0.13.2
     aiosqlite==0.15.0
     appdirs==1.4.4
@@ -45,7 +45,7 @@ install_requires =
     colorama==0.4.3
     commonmark==0.9.1
     contextlib2==0.6.0.post1
-    discord.py==1.5.1
+    discord.py==1.6.0
     distro==1.5.0; sys_platform == "linux"
     fuzzywuzzy==0.18.0
     idna==2.10
@@ -56,7 +56,7 @@ install_requires =
     python-Levenshtein-wheels==0.13.1
     pytz==2020.1
     PyYAML==5.3.1
-    Red-Lavalink==0.7.1
+    Red-Lavalink==0.7.2
     rich==9.5.1
     schema==0.7.2
     six==1.15.0