Remove confusing API index pages in Qiskit 0.19 (#1258)

## Problem

This is how Qiskit 0.19 looks:

<img width="260" alt="Screenshot 2024-04-29 at 5 00 14 PM"
src="https://github.com/Qiskit/documentation/assets/14852634/151d56df-09d2-47c6-885b-a8ce6f6e931a">

The three `qiskit` entries are:

https://docs.quantum.ibm.com/api/qiskit/0.19
https://docs.quantum.ibm.com/api/qiskit/0.19/ibmq-provider
https://docs.quantum.ibm.com/api/qiskit/0.19/aqua

0.19 is the only version like that, e.g. Qiskit 0.24 doesn't have
duplicates:

<img width="266" alt="Screenshot 2024-04-29 at 5 00 36 PM"
src="https://github.com/Qiskit/documentation/assets/14852634/93f4c64e-7427-41d3-9deb-ae8f5ebcd758">

In 0.19 docs, the first two `qiskit` entries are index pages for Qiskit
Aqua and Qiskit IBMQ Provider. Those are index pages that simply list
all modules, rather than module overview pages that describe the modules
`qiskit.aqua` and `qiskit.providers.ibmq`.

Having the three duplicate `qiskit` entries is going to be a problem
with #1211 when we group
modules.

## Solution

I simply deleted the two index files from the HTML and regenerated the
docs. If we like this PR, I will upload that HTML change to Box.

I went with deletion because it's the simplest fix. We don't have these
index pages in every version after 0.19, and it works fine.
#1211 will also help with
module discovery through better grouping.

We could instead rewrite the HTML for the two problematic files, but I
figured it's fine to do the simpler approach that's consistent with
later versions.

docs/api/qiskit/0.19/_toc.json

@@ -1,14 +1,6 @@
 {
   "title": "Qiskit SDK",
   "children": [
-    {
-      "title": "qiskit",
-      "url": "/api/qiskit/0.19/aqua"
-    },
-    {
-      "title": "qiskit",
-      "url": "/api/qiskit/0.19/ibmq-provider"
-    },
     {
       "title": "qiskit",
       "url": "/api/qiskit/0.19"