Fixes #1473: Fixes constraints on settings table cell

[janicelee]

Addresses issue described in: #1473

Based on the implementation of the table headers, it seems like we can avoid making constraints based on textLabel and instead give the spacerView the same width as used for the table headers.

Note: Noticed recent changes to master might be causing problems in displaying the settings table cells , created a separate issue for this here: #1592

[mozillamobilebot]

SwiftLint found issues

Warnings

File	Line	Reason
SettingsViewController.swift	109	Lines should not have trailing whitespace.
SettingsViewController.swift	112	Lines should not have trailing whitespace.
SettingsViewController.swift	117	Lines should not have trailing whitespace.
SettingsViewController.swift	122	Lines should not have trailing whitespace.
SettingsViewController.swift	129	Lines should not have trailing whitespace.
SettingsViewController.swift	132	Lines should not have trailing whitespace.
SettingsViewController.swift	135	Lines should not have trailing whitespace.
SettingsViewController.swift	139	Lines should not have trailing whitespace.
SettingsViewController.swift	141	Lines should not have trailing whitespace.
SettingsViewController.swift	152	Lines should not have trailing whitespace.
SettingsViewController.swift	158	Lines should not have trailing whitespace.
SettingsViewController.swift	163	Lines should not have trailing whitespace.
SettingsViewController.swift	168	Lines should not have trailing whitespace.
SettingsViewController.swift	174	Lines should not have trailing whitespace.
SettingsViewController.swift	179	Lines should not have trailing whitespace.
SettingsViewController.swift	184	Lines should not have trailing whitespace.
SettingsViewController.swift	190	Lines should not have trailing whitespace.
SettingsViewController.swift	194	Lines should not have trailing whitespace.
SettingsViewController.swift	198	Lines should not have trailing whitespace.
SettingsViewController.swift	467	Lines should not have trailing whitespace.

Generated by 🚫 Danger

[sblatz]

Looks good. Thanks for the fix (and for filing that other issue!)