Remove implicit this capture in lambdas

What does this implement/fix?

When declaring a lambda with a value-capture default [=, ...], the this pointer is implicitly captured by value as well. This results in potentially-unintuitive behavior (https://reviews.llvm.org/D142639) and produces a warning in newer versions of clang.

There were a few instances of capture in `unsupported/Eigen/CXX11/src/Tensor/ This simply makes the implicit captures explicit, preventing the warning. It does not change the compiled code at all, since it's just removing some syntactic sugar.