[Desktop] no hover text for Tip button on Twitter

[LaurenWags]

Description

When you hover over the in-line tip button on Twitter there's no hover text (ex. "Send a tip" or similar). This hover text does appear for GitHub in-line tip buttons.

Steps to Reproduce

1. Have Rewards enabled
2. Navigate to a twitter page (ex. twitter.com/emerick)
3. Look for Tip button (note, if you don't see any text saying "Tip", you've encountered [Desktop] race condition with Greaselion and localizations #12264 and need to restart your browser)
4. Hover over Tip button/text

Actual result:

"Tip" changes to orange, but no hover text:

Expected result:

Something similar to GH:

Reproduces how often:

easily

Brave version (brave://version info)

Brave	1.17.62 Chromium: 86.0.4240.185 (Official Build) dev (x86_64)
Revision	37e6f852ed18086458552039ad26421aa9fc7acc-refs/branch-heads/4240@{#1377}
OS	macOS Version 10.14.6 (Build 18G6032)

Version/Channel Information:

• Can you reproduce this issue with the current release? yes, 1.16.x
• Can you reproduce this issue with the beta channel? yes, 1.17.x
• Can you reproduce this issue with the nightly channel? yes, 1.18.x

Other Additional Information:

• Does the issue resolve itself when disabling Brave Shields? n/a
• Does the issue resolve itself when disabling Brave Rewards? n/a
• Is the issue reproducible on the latest version of Chrome? n/a

Miscellaneous Information:

cc @emerick @NejcZdovc

[emerick]

I believe we were relying on Twitter's standard CSS and definitions for this, but they removed all of the hover text on their buttons from what I can tell. Not sure if we should also follow suit, especially given that the button already says "Tip".

[Miyayes]

@mkarolin Will just remove tooltips since there are issues on some sites where tooltips can't appear.