Revert "Fixes microsoft#152785"

This ended up causing an issue where terminals could not be destroyed.

This reverts commit 8beecf1.

Author: Tyriar

src/vs/workbench/contrib/terminal/browser/terminalInstance.ts

@@ -1312,11 +1312,6 @@ export class TerminalInstance extends Disposable implements ITerminalInstance {
 
 
 	override dispose(immediate?: boolean): void {
-		if (this._isDisposed) {
-			return;
-		}
-		this._isDisposed = true;
-
 		this._logService.trace(`terminalInstance#dispose (instanceId: ${this.instanceId})`);
 		dispose(this._linkManager);
 		this._linkManager = undefined;
@@ -1355,8 +1350,10 @@ export class TerminalInstance extends Disposable implements ITerminalInstance {
 		// hasn't happened yet
 		this._onProcessExit(undefined);
 
-		this._onDisposed.fire(this);
-
+		if (!this._isDisposed) {
+			this._isDisposed = true;
+			this._onDisposed.fire(this);
+		}
 		super.dispose();
 	}