Welcome Screens are too tall for small screens

[bradleyrichter]

Remove top margin on the right place to reduce stackup height.

[btlechowski]

This is very annoying issue which prevents using brave://welcome page on small screens. The reason is that bottom navbar is not visible.

Tested on

Brave	0.69.128 Chromium: 77.0.3865.75 (Official Build) (64-bit)
Revision	201e747d032611c5f2785cae06e894cf85be7f8a-refs/branch-heads/3865@{#776}
OS	Ubuntu 18.04 LTS

[btlechowski]

Verification passed on

Brave	0.70.110 Chromium: 77.0.3865.90 (Official Build) beta (64-bit)
Revision	58c425ba843df2918d9d4b409331972646c393dd-refs/branch-heads/3865@{#830}
OS	Ubuntu 18.04 LTS

welcome page fits small screen

Scrollbar is shown when needed

Verified passed with

Brave	0.70.111 Chromium: 77.0.3865.90 (Official Build) beta (64-bit)
Revision	58c425ba843df2918d9d4b409331972646c393dd-refs/branch-heads/3865@{#830}
OS	macOS Version 10.13.6 (Build 17G5019)

• Confirmed that when I resize my window to be small the scroll bar appears when needed. Scrollbar is not displayed when window is large enough.

Verification passed on

Brave	0.70.116 Chromium: 77.0.3865.90 (Official Build) beta (64-bit)
Revision	58c425ba843df2918d9d4b409331972646c393dd-refs/branch-heads/3865@{#830}
OS	Windows 10 OS Version 1803 (Build 17134.1006)

• Confirmed that when I resize my window to be small the scroll bar appears when needed. Scrollbar is not displayed when window is large enough.