devel/ccls: unbreak with DEFAULT_VERSIONS+=llvm=-devel

Don't try hard to make LIB_DEPENDS pick the specific version when this
is already enforced by BUILD_DEPENDS. The left field in _DEPENDS lines
isn't recorded into binary packages, anyway.

<phase: lib-depends >

> ccls-0.20190301_2 depends on shared library: libLLVM--devel.so - not found

> Installing existing package /packages/All/llvm-devel-9.0.d20190226.txz

[120i386-default-llvm90-job-07] Installing llvm-devel-9.0.d20190226...
the most recent version of llvm-devel-9.0.d20190226 is already installed

> ccls-0.20190301_2 depends on shared library: libLLVM--devel.so - not found

• Error code 1