Bug 1104198 - Make DESKTOP builds work with mulet, remove DESKTOP_SHIMS.
Revert "Merge pull request #26679 from eliperelman/bug-1088118" for linter and gaia-unit test failures

This reverts commit aa5e5c6a81321f2fd1816854cecfeb7646a62fae, reversing
changes made to a7cdad97667823160bb785843e95358b887a5b32.
Merge pull request #26752 from eeejay/bug-1104198-take-3

Bug 1104198 - Make DESKTOP builds work with mulet, remove DESKTOP_SHIMS. r=ochameau