Start shared lib only if rewards is enabled

[NejcZdovc]

We should check preferences (now that we have it) if rewards is enabled or not. If it's not we should not start shared lib.

[LaurenWags]

Verified passed with

Brave | 1.12.105 Chromium: 84.0.4147.105 (Official Build) (64-bit)
-- | --
Revision | a6b12dfad6663f13a7e16e9a42a6a4975374096b-refs/branch-heads/4147@{#943}
OS | macOS Version 10.14.6 (Build 18G3020)

• Verified test plan from Do not start process if rewards is off brave-core#5924

Clean profile, Rewards not enabled, confirmed BAT Ledger Service is not running:

Enabled Rewards, confirmed BAT Ledger Service is running:

Confirmed able to claim UGP grant:

Disabled Rewards, confirmed BAT Ledger Service is not running:

• Encountered and logged [Desktop] re-enabling Rewards from panel doesn't work #11038 - re-enabling Rewards from panel doesn't work but looks like it did
• Encountered and logged [Desktop] re-enabling Rewards from NTP widget doesn't update display of widget #11039 - re-enabling Rewards from NTP widget doesn't look like it works but it did

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Verification passed on

Brave | 1.12.105 Chromium: 84.0.4147.105 (Official Build) (64-bit)
-- | --
Revision | a6b12dfad6663f13a7e16e9a42a6a4975374096b-refs/branch-heads/4147@{#943}
OS | Windows 10 OS Version 1903 (Build 18362.959)

• Verified test plan from Do not start process if rewards is off brave-core#5924

Clean profile, Rewards not enabled, confirmed BAT Ledger Service is not running:

Enabled Rewards, confirmed BAT Ledger Service is running:

Confirmed able to claim UGP grant:

Disabled Rewards, confirmed BAT Ledger Service is not running:

• Encountered [Desktop] re-enabling Rewards from panel doesn't work #11038 and [Desktop] re-enabling Rewards from NTP widget doesn't update display of widget #11039

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Verification passed on

Brave	1.12.105 Chromium: 84.0.4147.105 (Official Build) (64-bit)
Revision	a6b12dfad6663f13a7e16e9a42a6a4975374096b-refs/branch-heads/4147@{#943}
OS	Ubuntu 18.04 LTS

• Verified test plan from Do not start process if rewards is off brave-core#5924

Clean profile, Rewards not enabled, confirmed BAT Ledger Service is not running:

Enabled Rewards, confirmed BAT Ledger Service is running:

Confirmed able to claim UGP grant:

Disabled Rewards, confirmed BAT Ledger Service is not running:

• Encountered [Desktop] re-enabling Rewards from panel doesn't work #11038 and [Desktop] re-enabling Rewards from NTP widget doesn't update display of widget #11039

[srirambv]

Verification passed on OnePlus 6T with Android 10 running 1.12.109 x64 build

• Verified toggle rewards on page and enabling it via panel updates the state correctly on panel and page

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Verification passed on Samsung Tab A with Android 10 running 1.12.109 x64 build

• Verified toggle rewards on page and enabling it via panel updates the state correctly on panel and page