Removes SpeedreaderAndroidStudy to have Speedreader in default state

[SergeyZhukovsky]

Resolves #1174

Test plan:

• make sure that there is no SpeedreaderAndroidStudy

[github-actions]

✅ Test Seed Generated Successfully

To apply the test seed:

1. Desktop: Launch the browser with --variations-pr=1175.
   Android: Set the command line to --variations-pr=1175 in debug menu, restart the browser.
   iOS: Set Variations PR to 1175 in Brave Core Switches debug menu, restart the browser.
2. Wait 5-10 seconds to fetch the seed.
3. Restart the browser to apply the seed.
4. Ensure Active Variations section at brave://version starts with the expected seed version (see below).

Seed Details

Parameter	Value
Version	pull/1175@946040acc17dafb1ddfb1e22062634a812558784
Uploaded	Fri, 09 Aug 2024 15:21:47 GMT
PR commit	5129544
Base commit	6a06002
Merge commit	946040a
Serial number	68345c0b61dbca78475a25e9dc12658e

[kjozwiak]

Uplift into production approved after deliberating with @brave/uplift-approvers.

[kjozwiak]

Nightly verification(s):

Verification PASSED on Pixel 6 running Android 15 using the following build(s):

Brave | 1.70.66 Chromium: 128.0.6613.27 (Official Build) canary (64-bit)
--- | ---
Revision | 667a3d64bcaa33f50347e567971f37eeb76758aa
OS | Android 15; Build/AP31.240617.010; 35; REL

• ensured that SpeedreaderAndroidStudy is not being displayed under brave://version

Example	Example

---

BETA verification(s):

Verification PASSED on Pixel 6 running Android 15 using the following build(s):

Brave | 1.69.142 Chromium: 127.0.6533.100 (Official Build) beta (64-bit)
--- | ---
Revision | 49f7b324ba3979781c47181a213f4547fffd3c8d
OS | Android 15; Build/AP31.240617.010; 35; REL

• ensured that SpeedreaderAndroidStudy is not being displayed under brave://version

Example	Example