Use TEXT rather than VARCHAR

While we're changing anyway

synapse/storage/schema/delta/40/pushers.sql

@@ -17,14 +17,14 @@ CREATE TABLE IF NOT EXISTS pushers2 (
     id BIGINT PRIMARY KEY,
     user_name TEXT NOT NULL,
     access_token BIGINT DEFAULT NULL,
-    profile_tag VARCHAR(32) NOT NULL,
-    kind VARCHAR(8) NOT NULL,
-    app_id VARCHAR(64) NOT NULL,
-    app_display_name VARCHAR(64) NOT NULL,
-    device_display_name VARCHAR(128) NOT NULL,
+    profile_tag TEXT NOT NULL,
+    kind TEXT NOT NULL,
+    app_id TEXT NOT NULL,
+    app_display_name TEXT NOT NULL,
+    device_display_name TEXT NOT NULL,
     pushkey TEXT NOT NULL,
     ts BIGINT NOT NULL,
-    lang VARCHAR(16),
+    lang TEXT,
     data TEXT,
     last_stream_ordering INTEGER,
     last_success BIGINT,