Add adp-xfiles license

[fmarier]

Now that abp-xfiles has added a LICENSE file to the repo (gioxx/xfiles#7), we should add it to brave-core.

[btlechowski]

Verification passed on

Brave	1.3.38 Chromium: 78.0.3904.108 (Official Build) nightly (64-bit)
Revision	4b26898a39ee037623a72fcfb77279fce0e7d648-refs/branch-heads/3904@{#889}
OS	Ubuntu 18.04 LTS

Verified test plan from brave/brave-core#3991

Verified passed with

Brave	1.3.85 Chromium: 79.0.3945.88 (Official Build) beta (64-bit)
Revision	c2a58a36b9411c80829b4b154bfcab97e581f1f3-refs/branch-heads/3945@{#954}
OS	macOS Version 10.14.6 (Build 18G103)

• Verified location of license from Add adp-xfiles license #6910 (comment)

Verification passed on

Brave	1.3.87 Chromium: 79.0.3945.117 (Official Build) beta (64-bit)
Revision	04f0a055010adab4484f7497fbfdbf312c307f1d-refs/branch-heads/3945@{#1019}
OS	Windows 10 OS Version 1803 (Build 17134.1006)

• Verified test plan from Add abp-xfiles license brave-core#3991
  

[LaurenWags]

@fmarier not seeing this on macOS, is this expected? not sure if this license is OS specific?

Brave	1.3.85 Chromium: 79.0.3945.88 (Official Build) beta (64-bit)
Revision	c2a58a36b9411c80829b4b154bfcab97e581f1f3-refs/branch-heads/3945@{#954}
OS	macOS Version 10.14.6 (Build 18G103)

[fmarier]

@LaurenWags The behavior when #7150 got fixed and uplifted.

The license for ABP X Files is now in the "Brave Ad Block" section:

[LaurenWags]

gotcha, thanks @fmarier !